Add configurable SQLite journal modes to SQLiteConfiguration

[fang-ling]

Motivation

SQLite journal mode has an impact on performance, concurrency, and durability characteristics. Exposing this as a configuration option allows users to:

• Enable WAL (write-ahead log) for better concurrency and throughput
• Match journal mode to deployment requirements (e.g. embedded, ephemeral, or high-performance workloads)
• Avoid relying on external PRAGMA setup

Modifications

1. Introduces a new SQLiteConfiguration.JournalMode enum covering all supported SQLite journal modes:

• DELETE: Delete journal mode (SQLite default). Journal file is deleted after each transaction.
• WAL: WAL (Write-Ahead Logging) mode. Provides better concurrency and performance.
• TRUNCATE: Truncate journal mode. Journal file is truncated to zero length instead of deleted.
• PERSIST: Persist journal mode. Journal file is left on disk but header is overwritten.
• MEMORY: Memory journal mode. Journal is stored in memory.
• OFF: No journal mode. No rollback capability (dangerous).

2. Adds a journalMode property to SQLiteConfiguration with a default of .delete during the initialization, preserving existing behavior.
3. Automatically applies the configured journal mode when a connection is opened via:

PRAGMA journal_mode = <mode>

Additionally, tests have been added to verify that each supported journal mode is correctly applied and that the journal mode configuration works alongside foreign key enforcement.

This change is fully backward-compatible and opt-in.

Future directions

SQLite has an experimental wal2 journal mode under active development. With the introduction of the JournalMode enum, supporting wal2 in the future would be a straightforward, non-breaking extension once it becomes stable and widely available.