feat: add Arrow support to SQLite and MySQL adapters

[cofin]

Summary

sqlite, aiosqlite, and asyncmy tests for select_to_arrow

Changes

Integration Tests (30 tests total - NEW)

• tests/integration/test_adapters/test_sqlite/test_arrow.py (10 tests)
• tests/integration/test_adapters/test_aiosqlite/test_arrow.py (10 tests)
• tests/integration/test_adapters/test_asyncmy/test_arrow.py (10 tests)

Test Coverage

All three adapters now have comprehensive Arrow integration tests covering:

• ✅ Basic Arrow table/batch queries
• ✅ Parameterized queries with Arrow results
• ✅ NULL value handling in Arrow format
• ✅ Empty result sets
• ✅ Large datasets (1000+ rows)
• ✅ Type preservation across database types
• ✅ Polars DataFrame conversion via Arrow
• ✅ Database-specific type handling:
  • SQLite: JSON as TEXT, INTEGER for booleans
  • MySQL: JSON type, DECIMAL, DATETIME, BOOLEAN

Implementation Details

All three adapters inherit Arrow support from the base driver class via select_to_arrow(), which uses the conversion path: execute() → dict → Arrow.

This provides good performance and compatibility while maintaining a consistent API across all adapters.

SQLite Specifics

• SQLite uses ? parameter style
• JSON stored as TEXT (string in Arrow)
• Booleans stored as INTEGER (0/1)
• REAL for floating point numbers

MySQL Specifics

• MySQL uses %s parameter style
• Native JSON type support
• DECIMAL for precise numeric values
• DATETIME for timestamps
• BOOLEAN type (stored as TINYINT)

Testing

• ✅ 30/30 tests passing (sqlite: 10/10, aiosqlite: 10/10, asyncmy: 10/10)
• ✅ All lint checks passing (mypy, pyright, ruff, slotscheck)
• ✅ Unique table names (arrow_*) prevent test collisions
• ✅ Proper async fixture typing with AsyncGenerator

Related Work

• Builds on feat: add Arrow support to PostgreSQL adapters #157 (PR4 - PostgreSQL Adapters)
• Follows feat: add native Arrow support for ADBC, DuckDB, and BigQuery adapters #156 (PR3 - Native Adapters)
• Uses foundation from feat: add select_to_arrow() to base driver classes #155 (PR2 - Base Drivers) and feat: add Arrow type system foundation for select_to_arrow() #154 (PR1 - Type System)

Progress

With this PR, we've now added Arrow support testing for:

• ✅ PostgreSQL: asyncpg, psycopg, psqlpy (PR4 feat: add Arrow support to PostgreSQL adapters #157)
• ✅ SQLite: sqlite, aiosqlite (PR5 - this PR)
• ✅ MySQL: asyncmy (PR7 - this PR)

Still remaining:

• PR8: Architecture documentation

Next Steps

After this PR merges:

• PR8: Architecture documentation