Reuse parsed value enclosures by default

[claell]

Summary

• Reuse parsed quote, brace, and safe bare enclosure styles in the default writer.
• Preserve established quote/brace style when users edit field values.
• Fall back to braces if a formerly bare integer is edited to ordinary text.
• Keep braces as the default for new programmatic values without parser metadata.
• Extend the enclosure matrix so stale no-enclosing metadata cannot authorize unsafe text.

Closes #592.

Validation

• Complete enclosure suite under warnings-as-errors: 928 passed, 2 skipped.
• Complete upstream suite: 2,588 passed, 4 skipped, with the four existing deprecation warnings in tests/test_entrypoint.py.
• Complete pre-commit hook suite: passed.

The safety rule also turns eight formerly skipped matrix combinations into executable assertions because ordinary text with stale bare metadata now has an unambiguous enclosed result.

Review note

This changes default formatting but preserves semantics and reduces unrelated diffs. Callers that require uniform braces can still configure AddEnclosingMiddleware(reuse_previous_enclosing=False, ...) explicitly.

The edited-bare guard is important: blindly applying no-enclosing parser metadata after a value changes can emit invalid BibTeX. An explicit field.enclosing = "no-enclosing" demand still takes precedence for callers intentionally supplying a valid bare expression.

AI assistance

This pull request was prepared with ChatGPT Codex using GPT-5.6 Sol with high reasoning effort. Codex assisted with default-policy analysis, unsafe-edit discovery, matrix refinement, and validation. Automated validation is not a substitute for maintainer review.