test(marmot): the state blob is v4 now that it carries staged proposals

Persisting the staged-proposal pool moved STATE_VERSION from 3 to 4, but
this assertion still pinned 3. It is the only test that reads the version
word directly, so nothing else caught it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016kCuA6tc4JQzHPCDd39GHq

quartz/src/jvmAndroidTest/kotlin/com/vitorpamplona/quartz/marmot/mls/MlsGroupStateTest.kt

@@ -173,14 +173,14 @@ class MlsGroupStateTest {
         val state = group.saveState()
         val bytes = state.encodeTls()
 
-        // First two bytes are the state version (uint16). v3 appends the
-        // direct-path node private keys; older blobs still decode, so the
-        // version only ever moves forward when the layout gains a field.
+        // First two bytes are the state version (uint16). v4 appends the
+        // staged-proposal pool; older blobs still decode, so the version only
+        // ever moves forward when the layout gains a field.
         val reader =
             com.vitorpamplona.quartz.marmot.mls.codec
                 .TlsReader(bytes)
         val version = reader.readUint16()
-        assertEquals(3, version)
+        assertEquals(4, version)
     }
 
     @Test