fix(logging): keep file tracebacks uncolored while stderr stays colored

[Question86]

Summary

This patch fixes the ANSI color leak into file logs while keeping colored tracebacks on stderr.

What changed

• better_exceptions/log.py
  • Patch formatters per-handler instead of mutating a shared formatter instance.
  • Apply colored traceback formatting only for StreamHandler targeting sys.stderr.
  • Apply uncolored traceback formatting for FileHandler.
  • Invalidate record.exc_text cache per formatter call so each handler can format exceptions independently.
  • Restore AssertionError.args after formatting to avoid side effects when the same exception is formatted by multiple handlers.
• test/test_file_logging.py
  • Adds regression coverage for the real bug scenario:
    • shared formatter instance across stderr and file handlers
    • both handler orders (stderr first / file first)
  • Asserts: stderr contains ANSI, file does not.
• test_all.sh
  • Executes test/test_file_logging.py as an assertion-style test.

Why this approach

The issue appears when multiple handlers share one formatter object and logging caches record.exc_text. Patching a formatter globally can make file handlers inherit ANSI escapes. This patch isolates formatter behavior per handler and prevents cache cross-contamination.

Closes #87

[Question86]

Follow-up on design choices:\n\n- This patch intentionally handles the shared-formatter case (same Formatter instance attached to stderr + file handlers), which is where ANSI leakage commonly appears in practice.\n- It clears
ecord.exc_text per formatter call so each handler can apply its own exception rendering policy (colored stderr vs plain file output).\n- It restores AssertionError.args after formatting to avoid cross-handler side effects when the same exception is formatted more than once.\n- Added regression coverage in est/test_file_logging.py for both handler orders (stderr-first and file-first).\n\nHappy to adjust style/scope if you prefer a narrower patch.