feat(render): complete opacity effects

[Kyle-Ye]

Summary

• Add opacity shape styles and the .opacity(_:) shorthand for style resolution, text preparation, fallback colors, and copied styles.
• Route opacity modifiers through the accessibility provider and expose provider selection within the package.
• Add API documentation and regression coverage for style levels, identity opacity, and boundary values.

Validation

• Passed 18 focused regression cases and five API visibility checks using cached dependencies.
• Passed documentation and whitespace checks. No full package build was run.

[tuist]

🛠️ Tuist Run Report 🛠️

Tests 🧪

Scheme	Status	Ran test modules	Commit
OpenSwiftUI	✅	7	cf7476d76

Builds 🔨

Scheme	Status	Duration	Commit
OpenSwiftUI	✅	1m 12s	cf7476d76

[codecov]

Codecov Report

❌ Patch coverage is 73.91304% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 30.90%. Comparing base (f8584b6) to head (4b362fc).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ftUICore/Render/RendererEffect/OpacityEffect.swift	73.91%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1129      +/-   ##
==========================================
+ Coverage   30.79%   30.90%   +0.11%     
==========================================
  Files         876      876              
  Lines       70857    70925      +68     
==========================================
+ Hits        21820    21919      +99     
+ Misses      49037    49006      -31     

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