Introduce vtab subpackage (modernc.org/sqlite/vtab) exposing Module, Table,...
- Introduce vtab subpackage (modernc.org/sqlite/vtab) exposing Module, Table, Cursor, and IndexInfo API for Go virtual tables.
- Wire vtab registration into the driver: vtab.RegisterModule installs modules globally and each new connection calls sqlite3_create_module_v2.
- Implement vtab trampolines for xCreate/xConnect/xBestIndex/xDisconnect/xDestroy/xOpen/xClose/xFilter/xNext/xEof/xColumn/xRowid.
- Map SQLite’s sqlite3_index_info into vtab.IndexInfo, including constraints, ORDER BY terms, and constraint usage (ArgIndex → xFilter argv[]).
- Add an in‑repo dummy vtab module and test (module_test.go) that validates registration, basic scanning, and constraint visibility.