Allow application-defined auditing of normalized gitignore segments

[sricharanreddycheruku]

Related to #131: implements the maintainer's suggested optional segment-auditing
hook without imposing hard-coded limits on normal patterns.

Add an overridable _audit_segments() class method to both gitignore pattern
classes. Existing PathSpec/GitIgnoreSpec pattern_factory arguments let applications
supply an audited subclass. The hook receives an immutable tuple after normalization
and before regex translation, including optimized regex-override patterns. Comments,
null patterns and precompiled expressions are not audited. Rejection exceptions
propagate unchanged regardless of the pattern-notation errors policy.

Document a subclass example and the hook's limitations: a wildcard-count policy is
application-defined and does not guarantee bounded matching time. Update API docs,
change history and strict typed-usage examples.

Validation:

• New auditing tests: 6 methods with 66 passing subtests. The same tests on the
  original source report 53 failures (including subtests), with 19 passing controls.
• Complete Python 3.12.14 and 3.14.7 suites with simple, RE2 and Hyperscan installed:
  238 passed, 1 skipped, 974 subtests passed on each.
• Python 3.9.25, the minimum supported version: 178 passed, 61 optional-backend skips.
• The project's unittest-discover command passes all 239 tests, with 1 skipped.
• Warning-as-error Sphinx HTML build passes.
• mypy and pyright pass for Python 3.14 targets, including the audited subclasses.
  Targeting Python 3.12 reports existing _typing.py fallback errors; the same mypy
  errors are reproduced on unchanged upstream source.