feat: add support for hexadecimal RGBA color format

[aza-ali]

Summary

Adds support for 4-digit and 8-digit hexadecimal color codes with alpha channel to the Color class, addressing issue #1849.

Users can now use colors like:

• #FF00FF80 (50% transparent magenta)
• #f0f8 (shorthand 4-digit RGBA)

Changes Made

Core Functionality

• Extended Color dataclass with optional a field (alpha channel, default 255)
• Updated _validate_color_hex() to accept lengths 3, 4, 6, and 8
• Modified from_hex() to parse 4-digit (#RGBA) and 8-digit (#RRGGBBAA) hex codes
• Updated as_hex() to return #RRGGBBAA format when alpha != 255, otherwise #RRGGBB

New Methods

• as_rgba() - returns RGBA tuple
• as_bgra() - returns BGRA tuple
• from_rgba_tuple() - creates Color from RGBA tuple
• from_bgra_tuple() - creates Color from BGRA tuple

Internal Updates

• Updated __eq__() and __hash__() to include alpha channel
• Comprehensive docstrings with examples for all new functionality

Testing

• Added 27 new unit tests covering:
  • Parsing 4-digit and 8-digit hex codes with alpha
  • Converting to/from RGBA and BGRA tuples
  • Round-trip conversions
  • Edge cases (alpha=0, alpha=255)
  • Invalid inputs
• All 795 tests pass successfully
• Pre-commit hooks pass (ruff, bandit, codespell, etc.)

Backward Compatibility

✅ Fully backward compatible - all existing code continues to work:

• Default alpha value is 255 (fully opaque)
• Existing 3-digit and 6-digit hex codes work as before
• as_hex() returns 6-digit format when alpha=255
• Public API remains unchanged

Resolves

Closes #1849

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76%. Comparing base (a6ee3e9) to head (5050b34).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2004   +/-   ##
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  Coverage       76%     76%           
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  Files           62      62           
  Lines         7547    7575   +28     
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+ Hits          5714    5743   +29     
+ Misses        1833    1832    -1     

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[Copilot]

Pull request overview

Adds alpha-channel support to supervision.draw.color.Color, enabling parsing/serialization of 4- and 8-digit hex color codes (#RGBA, #RRGGBBAA) and providing RGBA/BGRA tuple helpers.

Changes:

• Extend Color with an a (alpha) channel and update hex validation/parsing to accept 3/4/6/8-digit formats.
• Update as_hex() to emit #RRGGBBAA when a != 255, and add RGBA/BGRA conversion helpers.
• Expand unit tests to cover new hex formats and tuple conversions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/supervision/draw/color.py	Implements RGBA support (alpha field, hex parsing/formatting, RGBA/BGRA helpers, equality/hash updates).
tests/draw/test_color.py	Adds/updates tests for RGBA hex parsing, as_hex() alpha behavior, and RGBA/BGRA tuple helpers.