Configure busy timeout on SQLite storage to prevent lock failures.

[davidz25]

On iOS, the SQLite C library defaults busy_timeout to 0 ms. When multiple connections access the same underlying database concurrently (such as an app and an app extension sharing an App Group container), any lock contention immediately throws SQLiteException: Error code: 5, message: database is locked.

Configure a default busy timeout of 5 seconds for SQLite connections on iOS:

• In SqliteStorage, accept a busyTimeout: Duration = 5.seconds parameter, validate that it is non-negative, and execute PRAGMA busy_timeout in the init block. Provide backward-compatible constructors.
• In IosStorage, delegate busyTimeout configuration to SqliteStorage, and provide secondary constructors with (storageFileUrl, excludeFromBackup) and (storageFileUrl, excludeFromBackup, busyTimeoutMs) overloads for Swift/Objective-C compatibility.
• In Storage, update KDoc to document concurrency and multi-instance safety guarantees across processes.
• In IosStorageTest, add unit test testBusyTimeout() reproducing the zero-timeout failure under lock contention, verifying that the default 5-second timeout waits and succeeds, and verifying that exceeding the timeout fails. Add testSqliteStorageBusyTimeout() verifying standalone SqliteStorage instances.
• In AndroidStorageTest, add testBusyTimeout() verifying that Android SQLite automatically configures a busy timeout (>= 2000 ms) and handles contention without error.

Fixes #1979.

Test: Ran ./gradlew :multipaz:jvmTest
Test: Ran ./gradlew :multipaz:iosSimulatorArm64Test
Test: Ran ./gradlew :multipaz:connectedDebugAndroidTest (on Pixel 8 Pro)
Test: Ran ./gradlew detekt
Test: Ran xcodebuild -project samples/SwiftTestApp/SwiftTestApp.xcodeproj -scheme SwiftTestApp -sdk iphonesimulator build