feat: support shorthand hex colors

[seapagan]

Summary

This PR adds support for 3-character shorthand hex colors in colored_text.

hex_to_rgb now accepts both the existing 6-digit forms and shorthand #rgb / rgb, expanding shorthand to the equivalent 6-digit color before parsing. Invalid lengths and malformed input continue to fall back to plain text.

The PR also updates crate docs, README examples, and examples/basic.rs to show equivalent hex forms, and removes the completed shorthand-hex item from TODO.md.

Summary by CodeRabbit

Release Notes

• New Features

  • Hex colour input now supports 3-digit shorthand formats (e.g., #f80) in addition to 6-digit formats.
  • Hex codes may now be provided with or without the leading # prefix.

• Documentation

  • Updated documentation and examples to reflect expanded hex colour format support.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 25acf9da-7cbd-4ee6-974d-c0027caf5bd4

📥 Commits

Reviewing files that changed from the base of the PR and between 37e8917 and 1ecfc80.

📒 Files selected for processing (6)

• README.md
• TODO.md
• examples/basic.rs
• src/color.rs
• src/lib.rs
• src/tests.rs

💤 Files with no reviewable changes (1)

• TODO.md

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📝 Walkthrough

Walkthrough

The pull request extends hex colour input support to accept 3-character shorthand formats (e.g., #f80) alongside the existing 6-character form. Updates include the hex_to_rgb function, documentation, tests, and examples.

Changes

Cohort / File(s)	Summary
Documentation Updates README.md, src/lib.rs	Expanded documentation to specify that .hex(code) accepts both #-prefixed and non-prefixed forms in 3-character shorthand or 6-character full formats. Updated examples to include valid shorthand ("#f80") and changed invalid examples from too-short to wrong-length inputs.
Core Implementation src/color.rs	Modified hex_to_rgb to accept both 3-digit and 6-digit hex strings by expanding 3-character inputs (duplicating each hex character) before parsing RGB values. Previous strict length check replaced with conditional branching.
Examples & Tests examples/basic.rs, src/tests.rs	Added four new println! examples demonstrating hex parsing without # prefix and 3-digit shorthand forms. Expanded test coverage in test_rgb_colors, test_hex_colors, and test_invalid_hex_returns_plain_text with shorthand and invalid-length cases.
Cleanup TODO.md	Removed completed TODO item for 3-character shorthand hex colour support.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• feat: modernize color composition and crate internals #5: Directly implements the 3-character shorthand hex colour parsing feature that was planned in that PR's colour module and documentation.

Poem

🐰 ✨ Hooray for hex so short and sweet!
Three digits now make colours complete,
#f80 shines bright with duplicated cheer,
Shorthand formats hopping far and near! 🎨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: support shorthand hex colors' accurately and concisely summarizes the main change—adding support for 3-character shorthand hex color formats across the crate.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/shorthand-hex-support

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