feat(commons): add iOS actuals for KmpLock, WeakReference, isValidUrl

Pre-stages the three iosMain actuals that the macOS CI run is most
likely to demand once it compiles :commons for Native (the dev
container can't extract the K/N LLVM toolchain to validate locally).

- KmpLock.ios.kt: NSRecursiveLock — mirrors the ReentrantLock
  semantics the jvmAndroid actual exposes (reentrant per-thread).
- WeakReference.ios.kt: actual typealias to kotlin.native.ref.
  WeakReference<T> — same constructor + get(): T? shape as the
  jvmAndroid typealias to java.lang.ref.WeakReference<T>.
- UrlValidation.ios.kt: NSURL.URLWithString with an explicit scheme
  check, since NSURL is more permissive than JVM's URI.toURL() and
  accepts scheme-less relatives that the JVM contract rejects.

Lands together so the next CI run's failure mode (if any) is more
informative than "iosArm64 unresolved reference" three times over.

commons/src/iosMain/kotlin/com/vitorpamplona/amethyst/commons/util/KmpLock.ios.kt

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.util
+
+import platform.Foundation.NSRecursiveLock
+
+actual class KmpLock {
+    // NSRecursiveLock mirrors ReentrantLock semantics on JVM/Android — a
+    // thread that already holds the lock can re-enter without deadlock.
+    private val delegate = NSRecursiveLock()
+
+    actual fun lock() = delegate.lock()
+
+    actual fun unlock() = delegate.unlock()
+}

commons/src/iosMain/kotlin/com/vitorpamplona/amethyst/commons/util/UrlValidation.ios.kt

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.util
+
+import platform.Foundation.NSURL
+
+actual fun isValidUrl(url: String?): Boolean {
+    if (url == null) return false
+    // NSURL.URLWithString returns null for syntactically invalid URLs. It is
+    // more permissive than JVM's URI(url).toURL() — it accepts scheme-less
+    // relative URLs ("foo", "/bar"). Match the JVM contract (absolute URL
+    // with a known scheme) by also requiring a non-empty scheme.
+    val nsUrl = NSURL.URLWithString(url) ?: return false
+    return !nsUrl.scheme.isNullOrEmpty()
+}

commons/src/iosMain/kotlin/com/vitorpamplona/amethyst/commons/util/WeakReference.ios.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.util
+
+actual typealias WeakReference<T> = kotlin.native.ref.WeakReference<T>