Add Text custom attribute support

[Kyle-Ye]

Agent Summary

• Add Text.Superscript and Text.CustomAttributes support

[augmentcode]

🤖 Augment PR Summary

Summary: This PR wires up initial support for attaching/querying custom text attributes and introduces a marker type for superscript.

Changes:

• Makes TextAttribute Hashable and adds Text.customAttribute(_:) to attach attributes via an internal text modifier
• Adds a TextAttributeModifierBase + generic modifier implementation that stores attributes into Text.Style.customAttributes
• Introduces SPI Text.CustomAttributes as a container with add and type-based subscript lookup
• Moves superscript/custom-attribute plumbing out of the AttributedString file and adds Text.Superscript as a standalone marker type

Technical Notes: Attribute transfer from AttributedString populates Text.Style.superscript and Text.Style.customAttributes for later renderer/layout consumption.

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[augmentcode]

Review completed. 1 suggestion posted.

Comment augment review to trigger a new review at any time.

[augmentcode]

The doc comment on customAttribute says “Only one attribute of each type … with inner attributes taking precedence”, but CustomAttributes.subscript returns the first match in attributes order and add/modify only append; if multiple values of the same TextAttribute type are present this will likely return the outer/earlier one instead of the inner/later one.

Severity: medium

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.71%. Comparing base (1278862) to head (8f1e074).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...OpenSwiftUICore/View/Text/Text/Text+Renderer.swift	0.00%	26 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #895      +/-   ##
==========================================
+ Coverage   26.68%   26.71%   +0.02%     
==========================================
  Files         694      697       +3     
  Lines       48683    48907     +224     
==========================================
+ Hits        12993    13065      +72     
- Misses      35690    35842     +152     

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