Add issue elixir-sqlite#192 test suite for deadlock and interrupt behavior

Comprehensive tests covering:
- sqlite3_interrupt aborts long-running SELECT/INSERT queries
- Connection remains usable after interrupt
- Interrupt + close race safety (PR elixir-sqlite#342 validation)
- Interrupt does NOT break through busy handler sleep
- Concurrent reads on single connection
- Single-connection isolation (sees own uncommitted writes)
- Implicit transaction staleness with WAL mode
- Close blocks on mutex until interrupt releases it
- WAL concurrent access patterns (reads, writes, deferred tx conflicts)
- DBConnection pool recovery after long query timeout (red - needs interrupt in disconnect)
- DBConnection pool recovery from busy handler deadlock (red - needs custom busy handler)
- Watchdog pattern for query timeout

Author: mjc