Fix exclusion patterns in Cython Box constructors

[MbappeWU]

A Cython-built Box raises TypeError: expected str, got re.Pattern when a string box_dots_exclude is propagated to nested boxes or reconstructed during copying. Box compiles the string internally, but its two constructor annotations and stubs only allow str | None.

Correct those signatures to str | re.Pattern[str] | None, matching the values already accepted by pure Python and passed through internal configuration. Keep the existing normalization and regex flags. Add regressions for both string and compiled-pattern inputs, nested mappings/lists, and copying.

Validation:

• Full pure-Python and fresh Cython suites: 161 passed each. Exact old compiled runtime: 2 regression failures / 1 passing control; final: 3 passed.
• Black 24.10.0, mypy, and all required pre-commit hooks passed. An installed-stub consumer accepts string/Pattern[str]/None and rejects integer/bytes inputs.
• Original 34-job Tests workflow passed, including all four manylinux targets. The CI snapshot has the exact same Git tree as this feature commit; no workflow files were changed.
• Built wheel/sdist integrity and all 16 tracked runtime files checked against the commit. Nineteen configuration scenarios match across source, the exact old pure-Python runtime, and the installed compiled wheel, including matching flags and copy results.

Those probes also record the existing option reset in BoxList.__deepcopy__; copied-child states match the pure-Python baseline rather than being reported as complete option preservation.

AI-assisted implementation and validation with Codex.

[MbappeWU]

Tidying up my open PRs, so I'm closing this one while the repo seems inactive. Feel free to ping me and I'll reopen or rebase.