refactor(quartz): add TimeUtils.nowMillis, drop raw System calls in pagers

The relay-paging trackers measured elapsed wall-clock with
System.currentTimeMillis() directly. Introduce a multiplatform millisecond
clock (currentTimeMillis expect/actual across jvm/android/ios/macos/linux,
mirroring the existing currentTimeSeconds) exposed as TimeUtils.nowMillis(),
and route PerRelayLoadTracker + WindowLoadTracker through it.

TimeUtils.now() is seconds, so it can't be used for the ms-scale silence /
idle / linger timers — nowMillis() is the correct primitive. No behavior
change (same underlying clock on JVM/Android).

Note: the two trackers stay in jvmAndroid for now — @Synchronized has no
commonMain equivalent. ConcurrentHashMap is kept deliberately: LargeCache is
a sorted ConcurrentSkipListMap (Comparable, compareTo-identity keys) and the
pager keys (ConvoKey not Comparable; ChatroomKey.compareTo is hashCode-based)
don't satisfy that, so ConcurrentHashMap is the correct structure here.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

quartz/src/androidMain/kotlin/com/vitorpamplona/quartz/utils/Platform.android.kt

@@ -23,3 +23,5 @@ package com.vitorpamplona.quartz.utils
 actual fun platform() = "Android"
 
 actual fun currentTimeSeconds() = System.currentTimeMillis() / 1000
+
+actual fun currentTimeMillis() = System.currentTimeMillis()

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/utils/Platform.kt

@@ -23,3 +23,5 @@ package com.vitorpamplona.quartz.utils
 expect fun platform(): String
 
 expect fun currentTimeSeconds(): Long
+
+expect fun currentTimeMillis(): Long

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/utils/TimeUtils.kt

@@ -36,6 +36,8 @@ object TimeUtils {
 
     fun now() = currentTimeSeconds()
 
+    fun nowMillis() = currentTimeMillis()
+
     fun tenSecondsFromNow() = now() + TEN_SECONDS
 
     fun tenSecondsAgo() = now() - TEN_SECONDS

quartz/src/iosMain/kotlin/com/vitorpamplona/quartz/utils/Platform.ios.kt

@@ -31,3 +31,5 @@ actual fun currentTimeSeconds(): Long {
     // NSDate().timeIntervalSince1970 returns seconds since 1970-01-01 00:00:00 UTC
     return (NSDate().timeIntervalSince1970).toLong()
 }
+
+actual fun currentTimeMillis(): Long = (NSDate().timeIntervalSince1970 * 1000).toLong()

quartz/src/jvmAndroid/kotlin/com/vitorpamplona/quartz/nip01Core/relay/client/paging/PerRelayLoadTracker.kt

@@ -22,6 +22,7 @@ package com.vitorpamplona.quartz.nip01Core.relay.client.paging
 
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.utils.Log
+import com.vitorpamplona.quartz.utils.TimeUtils
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.delay
@@ -82,14 +83,14 @@ class PerRelayLoadTracker(
         clearJob?.cancel() // a new page is starting — keep the spinner up, no flicker
         clearJob = null
         inFlight.add(relay)
-        lastActivityMs = System.currentTimeMillis()
+        lastActivityMs = TimeUtils.nowMillis()
         _loading.value = true
         ensureWatchdog()
     }
 
     /** A sign of life from a relay (an event). Keeps the silence watchdog from firing. */
     fun onActivity() {
-        lastActivityMs = System.currentTimeMillis()
+        lastActivityMs = TimeUtils.nowMillis()
     }
 
     /**
@@ -101,7 +102,7 @@ class PerRelayLoadTracker(
      */
     @Synchronized
     fun onSettled(relay: NormalizedRelayUrl) {
-        lastActivityMs = System.currentTimeMillis()
+        lastActivityMs = TimeUtils.nowMillis()
         if (inFlight.remove(relay) && inFlight.isEmpty()) scheduleClear()
     }
 
@@ -141,7 +142,7 @@ class PerRelayLoadTracker(
                     delay(WATCHDOG_TICK_MS)
                     val silenced =
                         synchronized(this@PerRelayLoadTracker) {
-                            if (inFlight.isNotEmpty() && System.currentTimeMillis() - lastActivityMs > silenceMs) {
+                            if (inFlight.isNotEmpty() && TimeUtils.nowMillis() - lastActivityMs > silenceMs) {
                                 val pending = inFlight.toSet()
                                 inFlight.clear()
                                 _loading.value = false

quartz/src/jvmAndroid/kotlin/com/vitorpamplona/quartz/nip01Core/relay/client/paging/WindowLoadTracker.kt

@@ -25,6 +25,7 @@ import com.vitorpamplona.quartz.nip01Core.relay.client.reqs.SubscriptionListener
 import com.vitorpamplona.quartz.nip01Core.relay.filters.Filter
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.utils.Log
+import com.vitorpamplona.quartz.utils.TimeUtils
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.delay
@@ -104,17 +105,17 @@ class WindowLoadTracker(
         expected = emptySet()
         heardFrom.clear()
         settled.clear()
-        lastActivityMs = System.currentTimeMillis()
+        lastActivityMs = TimeUtils.nowMillis()
         val wasLoading = _loading.value
         _loading.value = true
         Log.d(TAG) { "[$name] load start" + if (!wasLoading) "" else " (restart)" }
         watchdog?.cancel()
         watchdog =
             scope.launch {
-                val deadline = System.currentTimeMillis() + absoluteCap.inWholeMilliseconds
+                val deadline = TimeUtils.nowMillis() + absoluteCap.inWholeMilliseconds
                 while (isActive) {
                     delay(IDLE_CHECK_MS)
-                    if (!tick(gen, System.currentTimeMillis(), deadline)) break
+                    if (!tick(gen, TimeUtils.nowMillis(), deadline)) break
                 }
             }
     }
@@ -164,7 +165,7 @@ class WindowLoadTracker(
     /** A non-terminal sign of life from [relay] (a stored or live event). Keeps the idle timer alive. */
     fun onRelayEvent(relay: NormalizedRelayUrl) {
         heardFrom.add(relay)
-        lastActivityMs = System.currentTimeMillis()
+        lastActivityMs = TimeUtils.nowMillis()
     }
 
     /**
@@ -173,7 +174,7 @@ class WindowLoadTracker(
      */
     @Synchronized
     fun onRelaySettled(relay: NormalizedRelayUrl) {
-        lastActivityMs = System.currentTimeMillis()
+        lastActivityMs = TimeUtils.nowMillis()
         heardFrom.add(relay)
         settled.add(relay)
         if (expected.isNotEmpty() && settled.containsAll(expected)) finish("all relays")

quartz/src/jvmMain/kotlin/com/vitorpamplona/quartz/utils/Platform.jvm.kt

@@ -23,3 +23,5 @@ package com.vitorpamplona.quartz.utils
 actual fun platform() = "JVM"
 
 actual fun currentTimeSeconds() = System.currentTimeMillis() / 1000
+
+actual fun currentTimeMillis() = System.currentTimeMillis()

quartz/src/linuxMain/kotlin/com/vitorpamplona/quartz/utils/Platform.linux.kt

@@ -38,3 +38,12 @@ actual fun currentTimeSeconds(): Long {
         return ts.tv_sec
     }
 }
+
+@OptIn(ExperimentalForeignApi::class)
+actual fun currentTimeMillis(): Long {
+    memScoped {
+        val ts = alloc<timespec>()
+        clock_gettime(CLOCK_REALTIME, ts.ptr)
+        return ts.tv_sec * 1000 + ts.tv_nsec / 1_000_000
+    }
+}

quartz/src/macosMain/kotlin/com/vitorpamplona/quartz/utils/Platform.macos.kt

@@ -26,3 +26,5 @@ import platform.Foundation.timeIntervalSince1970
 actual fun platform() = "macOS"
 
 actual fun currentTimeSeconds(): Long = (NSDate().timeIntervalSince1970).toLong()
+
+actual fun currentTimeMillis(): Long = (NSDate().timeIntervalSince1970 * 1000).toLong()