Keep file logging tracebacks uncolored

[dicnunz]

Fixes #87.

IssueHunt bounty: https://issuehunt.io/r/Qix-/better-exceptions/issues/87

This is a fresh, tested replacement for the stale direction in #99. That PR is still dirty/stale and had requested changes; this keeps the scope limited to the logging color behavior.

Reproduction

When a logger has both a stderr StreamHandler and a FileHandler, logging formats the same LogRecord for each handler. If the stream handler formats first, logging caches record.exc_text with ANSI color codes, and the file handler can reuse that colored cached traceback.

Changes

• Adds a colored= parameter to better_exceptions.format_exception().
• Patches each logging handler formatter with the right exception formatter: stderr stream handlers keep color, file handlers use uncolored traceback formatting.
• Clears and restores record.exc_text while formatting exceptions so each handler recomputes traceback text with its own color policy.
• Adds a regression test that asserts stream output remains colored while file output has no ANSI escapes.

Tests

Passed:

• FORCE_COLOR=1 TERM=xterm PYTHONPATH=. python3 test/test_file_logging.py
• python3 -m py_compile better_exceptions/init.py better_exceptions/log.py test/test_file_logging.py
• Manual handler-order smoke test: stream-first and file-first both produced file_ansi=False and stream_ansi=True.

Not fully completed locally:

• PYTHON=python3 ./test_all.sh: this machine does not have the repo's expected python command available by default, and under the available Python 3.14 the existing golden-output normalizer does not normalize truncated module reprs. The new regression test above is direct and passing.

[dicnunz]

Pushed ba53553 with two merge-readiness fixes: shared Formatter instances are now cloned per handler, and AssertionError.args is restored after each logging formatter pass so colored assertion text cannot leak between handlers. I also moved the silent regression into assert_case so the full golden-output suite continues after it.

Verified:

• FORCE_COLOR=1 TERM=xterm PYTHONPATH=. python3 test/test_file_logging.py
• python3 -m py_compile better_exceptions/__init__.py better_exceptions/log.py test/test_file_logging.py
• from a short /tmp/be149 copy with a python -> python3 shim: PYTHON=python3 BETEXC_PYTHON=python ./test_all.sh