MudColor: Make H, S, L readonly

[ScarletKuro]

Description

Just small improvement that makes MudColor truly safe immutable, Before you could accidentally change HSL values because of private set, now they are protected against unexpected modifications.

Type of Changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation (fix or improvement to the website or code docs)

Checklist

• [x] The PR is submitted to the correct branch (dev).
• [x] My code follows the code style of this project.
• [ ] I've added relevant tests.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.09%. Comparing base (28bc599) to head (25273d3). Report is 118 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #8823 +/- ## ========================================== + Coverage 89.82% 90.09% +0.26% ========================================== Files 412 421 +9 Lines 11878 12211 +333 Branches 2364 2409 +45 ========================================== + Hits 10670 11002 +332 + Misses 681 666 -15 - Partials 527 543 +16 ```

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