Refactor SQLovely internals

[MayerTim]

Summary

Refactor SQLovely internals to make formatter, diagnostics, metadata handling, tests, and project quality checks easier to maintain.

This branch keeps formatter and metadata behavior stable while reorganizing the implementation into clearer internal modules.

Changes

• Isolate the SQL formatting pipeline from the main formatter entry point.
• Group Watcom formatter passes into structural and cleanup phases.
• Centralize shared formatter context and safety handling.
• Debounce SQL document diagnostics and avoid expensive metadata diagnostics on very large documents.
• Split metadata header parsing, rendering, placement, history, and legacy migration internals.
• Organize formatter regression tests into focused topic-based suites.
• Extract formatter indentation logic into a dedicated indentation engine.
• Add formatter pipeline documentation.
• Add project quality tooling for formatting, linting, and typechecking.
• Streamline CI validation so source checks, tests, and packaging run without duplicate validation work.

Validation

• npm run check
• npm test
• node ./scripts/packageVsix.js