tests: backslash+bracket regression guards; xfail raw backslash-before-[ bug (#2993)

[lesliehc]

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

AI?

• AI was used to generate this PR

Description

This is tests-only. It documents and guards behavior around backslashes with Rich markup:

• Ensure backslash-escaped brackets render literally and don’t cause mismatched tags:
  • r"[b]hello[/b]"
  • r"C:[bin]\tools"
  • r"C:\[bin]\tools"
  • r"[color(123,45,6)]x[/color]"
• Add an xfail for a known issue where a raw backslash immediately before [ is swallowed:
  • r"C:[tmp]\file.txt"
  • Marked @pytest.mark.xfail(strict=False) so this turns green automatically when fixed.

No runtime code is changed.

Files changed

• tests/test_markup_backslash_escape.py (new)

Local test evidence

poetry run pytest -q tests/test_markup_backslash_escape.py
6 passed, 1 xfailed in 0.04s

Issue link

• References: [BUG] Text.markup fails to escape backslashes #2993

Notes

• Happy to split the xfail into a separate file or tweak parametrization if preferred.

Checklist

• Ran black (default args) on new test file
• Added tests
• I accept that @willmcgugan may be pedantic in the code review