refactor(quartz): swap FsEventStore clock ctor param for protected now()

The clock injection existed only for NIP-40 expiration tests. A public
constructor parameter that ~every caller ignores is API clutter, so
move it to a subclass seam:

- FsEventStore is now `open class`; no more `clock: () -> Long` param.
- `protected open fun now(): Long = TimeUtils.now()` is the override
  point. Production always takes the default; tests subclass.
- FsExpirationTest gains a private `ClockedStore(root, source)` that
  overrides `now()`. Semantics unchanged, all 113 fs tests still green.

Public `FsEventStore` ctor is now `(root, indexingStrategy, relay)` —
no behavioural-drift surface that callers have to learn.

quartz/src/jvmMain/kotlin/com/vitorpamplona/quartz/nip01Core/store/fs/FsEventStore.kt

@@ -57,14 +57,9 @@ import kotlin.io.path.readText
  * addressable slots, NIP-09 tombstones, NIP-40 expiration, NIP-50 FTS,
  * NIP-62 vanish, transactions, scrub.
  */
-class FsEventStore(
+open class FsEventStore(
     val root: Path,
     indexingStrategy: IndexingStrategy = DefaultIndexingStrategy(),
-    /**
-     * Source of "now" in unix seconds. Injectable so tests can drive
-     * NIP-40 expiration deterministically. Defaults to `TimeUtils.now()`.
-     */
-    private val clock: () -> Long = { TimeUtils.now() },
     /**
      * Optional relay URL the store is acting on behalf of. Used by
      * NIP-62 [RequestToVanishEvent.shouldVanishFrom] scoping. When
@@ -153,6 +148,14 @@ class FsEventStore(
         }
     }
 
+    /**
+     * Source of "now" in unix seconds. Defaults to [TimeUtils.now]; tests
+     * override this via a subclass so NIP-40 expiration behaviour (insert
+     * guard and periodic sweep) can be driven deterministically without
+     * waiting on the wall clock or patching a global time source.
+     */
+    protected open fun now(): Long = TimeUtils.now()
+
     /**
      * NIP-40 pre-insert guard. Parity with SQLite's `reject_expired_events`
      * trigger: an event whose expiration tag is `<= now` is rejected
@@ -162,7 +165,7 @@ class FsEventStore(
     private fun isAlreadyExpired(event: Event): Boolean {
         val exp = event.expiration() ?: return false
         if (exp <= 0) return false
-        return exp <= clock()
+        return exp <= now()
     }
 
     /**
@@ -384,7 +387,7 @@ class FsEventStore(
     override fun deleteExpiredEvents() =
         lockManager.withWriteLock {
             if (!Files.isDirectory(layout.idxExpiresAt)) return@withWriteLock
-            val now = clock()
+            val now = now()
             val toDelete = ArrayList<HexKey>()
             Files.list(layout.idxExpiresAt).use { stream ->
                 for (entry in stream) {

quartz/src/jvmMain/kotlin/com/vitorpamplona/quartz/nip01Core/store/fs/README.md

@@ -130,8 +130,6 @@ val store = FsEventStore(
     root = Path.of(System.getProperty("user.home"), ".amy", "events-store"),
     // optional NIP-62 relay scoping; null = only ALL_RELAYS vanish requests cascade
     relay = null,
-    // optional clock for tests
-    clock = { com.vitorpamplona.quartz.utils.TimeUtils.now() },
 )
 ```
 
@@ -140,6 +138,11 @@ bytes) is generated atomically on first open and read on every
 subsequent open — it salts every tag / owner hash, so it must persist
 or every previously-written index entry becomes unreachable.
 
+`FsEventStore` is `open` and exposes a `protected open fun now(): Long
+= TimeUtils.now()`. Tests override it with a subclass to drive NIP-40
+expiration at exact timestamps without relying on the wall clock; see
+`FsExpirationTest.ClockedStore`.
+
 ### Insert
 
 ```kotlin

quartz/src/jvmTest/kotlin/com/vitorpamplona/quartz/nip01Core/store/fs/FsExpirationTest.kt

@@ -40,13 +40,24 @@ class FsExpirationTest {
     private lateinit var root: Path
     private var clockNow: Long = 1_000_000
 
-    private lateinit var store: FsEventStore
+    /**
+     * Test subclass overriding the `now()` seam so we can drive NIP-40
+     * expiration at exact timestamps — no wall-clock sleeps, no flakes.
+     */
+    private class ClockedStore(
+        root: Path,
+        private val source: () -> Long,
+    ) : FsEventStore(root) {
+        override fun now(): Long = source()
+    }
+
+    private lateinit var store: ClockedStore
 
     @BeforeTest
     fun setup() {
         Secp256k1Instance
         root = Files.createTempDirectory("fs-exp-")
-        store = FsEventStore(root, clock = { clockNow })
+        store = ClockedStore(root) { clockNow }
     }
 
     @AfterTest