Review query escaping and add test coverage

[JanJakes]

Review strings escaping in the MySQL lexer and SQLite driver, and add a comprehensive test suite.

1. Verify string literal escaping (https://github.com/Automattic/sqlite-database-integration/pull/1#discussion_r1935826325).
2. Add a comprehensive test suite (https://github.com/Automattic/sqlite-database-integration/pull/1#discussion_r1935822420).
3. Consider unescaping MySQL queries in lexer (https://github.com/Automattic/sqlite-database-integration/pull/1#discussion_r1935819358).