Add colour to vulture CLI output

[hugovk]

Description

https://github.com/albertas/deadcode has colour output, but is unmaintained and doesn't support Python 3.14.

This PR adds colour to vulture's CLI output to make it easier to read:

This uses a colour scheme similar to flake8, so will be familiar to people.

It adds a -c, --color {yes,no,auto} option, defaulting to auto.

It uses the termcolor library, which disables colour when not in a TTY, so piped output has no ANSI codes. It also respects common env vars such as NO_COLOR=1 and FORCE_COLOR=1: https://github.com/termcolor/termcolor#overrides

Related Issue

Checklist:

• I have updated the documentation in the README.md file or my changes don't require an update.
• I have added an entry in CHANGELOG.md.
• I have added or adapted tests to cover my changes.
• I have run pre-commit run --all-files to format and lint my code.

[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.52%. Comparing base (81fb2ac) to head (6fcc1a6).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
vulture/config.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #415      +/-   ##
==========================================
+ Coverage   93.46%   93.52%   +0.06%     
==========================================
  Files           9        9              
  Lines         597      618      +21     
==========================================
+ Hits          558      578      +20     
- Misses         39       40       +1     

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