fix(quartz/sqlite): set busy_timeout to deflake reader+writer races

Without busy_timeout SQLite returns SQLITE_BUSY immediately when
BEGIN IMMEDIATE can't acquire a lock — e.g. during a WAL
auto-checkpoint or a reader briefly upgrading its snapshot — instead
of retrying. ParallelInsertTest's reader+writer test hit this ~10%
of runs. 5s matches Room's default and adds no overhead in the
uncontended case.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip01Core/store/sqlite/SQLiteEventStore.kt

@@ -106,6 +106,13 @@ class SQLiteEventStore(
                 // The DB can be corrupted if the OS shuts down before
                 // sync, which generally doesn't happen on Android.
                 db.execSQL("PRAGMA synchronous = OFF;")
+
+                // Without busy_timeout, BEGIN IMMEDIATE returns SQLITE_BUSY
+                // the instant another connection holds a conflicting lock —
+                // e.g. a WAL auto-checkpoint or a reader transiently
+                // upgrading its snapshot. With it, SQLite retries internally
+                // for up to N ms before giving up. Matches Room's default.
+                db.execSQL("PRAGMA busy_timeout = 5000;")
             },
             onMigrate = { db ->
                 val currentVersion = getUserVersion(db)