Fix two crashes from unguarded calls into the optional Rich dependency

[pranjalm37]

Summary

Fixes #655 and #576. Both are crashes caused by calling into the optional
rich dependency without the same defensive handling structlog applies
elsewhere.

#655 — to_repr() propagates exceptions from Rich's introspection

rich.pretty.traverse(...).render() was called with no error handling,
unlike the non-Rich fallback path right below it, which explicitly catches
everything ("Also catch all errors, similarly to safe_str()"). If Rich's
own object introspection raises (e.g. on an object with unusual attribute
access, as in the anyio-internal object from the report), the exception
propagates out of to_repr() and breaks exception logging entirely — at
exactly the moment you need it most.

Fix: wrap the Rich call in try/except and fall back to the manual repr
algorithm on failure, so to_repr() actually honors its own docstring
("Get repr string for an object, but catch errors").

#576 — RichTracebackFormatter crashes on older Rich versions

RichTracebackFormatter.__call__() always passes locals_hide_dunder and
locals_hide_sunder to Traceback.from_exception(). Those arguments were
only added in Rich 13.1.0, so on older Rich (e.g. 13.0.1, as in the report)
this raises TypeError: Traceback.from_exception() got an unexpected keyword argument 'locals_hide_dunder', crashing the console renderer
outright.

Fix: inspect Traceback.from_exception's signature once (module-level,
next to the existing Rich import) and only pass the kwargs the installed
Rich version actually supports — mirroring the hasattr(tb, "code_width")
compatibility check already a few lines below, which exists for the same
reason (forward compat with code_width in that case, backward compat
with these two here).

Test plan

• test_to_repr_rich_error — monkeypatches rich.pretty.traverse to
  raise and asserts to_repr() still returns a correct plain repr
  instead of propagating.
• test_old_rich_missing_locals_hide_params — monkeypatches the
  supported-params set to simulate an old Rich install and asserts
  locals_hide_dunder/locals_hide_sunder are omitted from the call.
• Manually reproduced Version compatibility check for optional dependencies #576 exactly by installing rich==13.0.1 locally
  and confirmed the TypeError before the fix / clean success after.
• Full suite: pytest tests/ → 902 passed, 21 skipped (up from 900
  passed pre-change — the 2 new tests).
• ruff check / ruff format clean on all changed files.
• Added a changelog entry under ## [Unreleased].

[codspeed-hq]

Merging this PR will not alter performance

✅ 10 untouched benchmarks

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_{Comparing pranjalm37:fix/rich-defensive-handling-655-576 (e9d9f21) with main (bf3cfd0)¹}

Footnotes

1. No successful run was found on main (ab24a26) during the generation of this report, so bf3cfd0 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩