fix(ReprHighlighter): highlight only standalone hex; support 0X/sign/underscores; add boundary tests

[troysis]

Type of changes

• [ x ] Bug fix
• New feature
• Documentation / docstrings
• [ x ] Tests
• Other

Checklist

• [ x ] I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• [ x ] I've added tests for new code.
• [ x ] I accept that @willmcgugan may be pedantic in the code review.

Description

Summary
Fixes false positives where ReprHighlighter highlighted embedded 0x… (e.g., 1920x1080). Tightens the regex to match standalone hex literals only, while supporting optional sign, uppercase 0X, and single underscore separators between digits.

Related issue
Fixes #3854

Regex

(?<![0-9A-Za-z_])[+-]?0[xX]0-9A-Fa-f*(?![0-9A-Za-z_])

Changes

rich/highlighter.py: updated hex branch in ReprHighlighter.

tests/test_highlighter.py: added expanded boundary cases (signs, 0X, underscores, punctuation boundaries, invalid underscores).

QA

Focused + full tests: pytest -q

Tooling: black, ruff, mypy clean on touched files

Scope

Scoped to ReprHighlighter; JSON highlighter unchanged.

[troysis]

Thanks for reviewing this!

This PR fixes false positives where ReprHighlighter highlighted embedded 0x… (e.g., 1920x1080).
I limited the change to ReprHighlighter only (JSON unchanged) and added boundary tests.

The current regex supports:

optional +/- sign

uppercase 0X as well as lowercase

single underscores between digits (PEP 515 style), while forbidding double/trailing underscores

If you’d prefer a simpler version (e.g., just boundary + 0X support without underscores), I’m happy to adjust quickly.