test(formatter): add metadata boundary corpus guards

[MayerTim]

Summary

• Add a Watcom corpus fixture for a SQLovely metadata header immediately after a procedure signature and before BEGIN.
• Add a Watcom corpus fixture for multiple objects with separate metadata headers in one script.
• Preserve object-name-like SQL text inside metadata comments, string literals, and comments.
• Preserve current formatter behavior with expected-output and idempotency checks.
• Keep this branch test-only with no formatter implementation, metadata logic, diagnostics, extension behavior, or formatter default changes.

Validation

• npm run test:corpus
• npm run validate
• npm run package:vsix

Notes

This PR fills the final small corpus coverage gap identified by the private coverage inventory. It does not change formatter implementation, metadata behavior, diagnostics behavior, formatter defaults, extension behavior, product behavior, or public documentation.