feat: Add with_opacity() helper for color opacity

[sojotype]

Summary

This PR adds support for a new hexa() color format that allows specifying colors with alpha transparency using a more readable percentage-based syntax.

Changes

• New feature: hexa(color,X%) format support
  • color can be accent (Windows accent color) or hex code
  • X% specifies opacity percentage (0-100%)
• Implementation: Added parse_hexa() function in src/colors.rs
• Documentation: Updated README.md and config.yaml with examples
• Tests: Added comprehensive test coverage for all hexa format variations

Examples

active_color: "hexa(accent,40%)"    # Windows accent with 40% opacity
active_color: "hexa(#ff0000,60%)"   # Red with 60% opacity
active_color: "hexa(00ff00,50%)"    # Green with 50% opacity (# optional)

Benefits

• More intuitive than hex alpha values (e.g., hexa(#ff0000,60%) vs #ff000099)
• Supports both accent colors and custom hex codes
• Alpha override functionality for existing hex codes with alpha

[lukeyou05]

Since hexa() can also be used for non-hex values (i.e. accent), and since percentages are more commonly seen when working with opacity rather than alpha, I wonder if it would be better to name it something like with_opacity(). Thoughts?

[sojotype]

Since hexa() can also be used for non-hex values (i.e. accent), and since percentages are more commonly seen when working with opacity rather than alpha, I wonder if it would be better to name it something like with_opacity(). Thoughts?

That makes sense) Thanks for the idea)

[lukeyou05]

We should probably move the parse_with_opacity() call outside get_color_from_hex() since the names are different now. I think the best way to do that would be to break out lines 426 - 432 into a separate function called something like get_color_with_opacity(), and then use that function in lines 85 and 108 (right next to the other get_accent_color() and get_color_from_hex() calls). That does lead to more repeated code but I could refactor that out in the future.

[lukeyou05]

The config section in the README is meant to track whatever is in the latest release, so we should revert everything here since it won't be released until later.