Update geometry and shape style

[Kyle-Ye]

Summary

Close #474

• Refine GeometryReader geometry handling and update the related example/UI test coverage.
• Add container shape support, including ContainerRelativeShape and container shape propagation.
• Add anchored shape style support and update background/overlay shape-style behavior.
• Improve background style propagation through view inputs so primary content receives the correct environment updates.

[augmentcode]

🤖 Augment PR Summary

Summary: This PR completes GeometryReader geometry handling and expands shape-style/background/overlay behavior to match SwiftUI semantics, including container-relative shapes and anchored shape styles.

Changes:

• Updates GeometryReader/GeometryProxy to properly resolve anchors, frames, scroll-view clipping, and sized coordinate-space bounds.
• Implements sized coordinate-space discovery in ViewTransform to support bounds(of:)-style queries.
• Adds container-shape infrastructure: ContainerRelativeShape, propagation via view inputs, and ImplicitContainerShape behavior.
• Introduces anchored shape style support via _AnchoredShapeStyle (including resolved paint plumbing).
• Reworks background modifiers to support style/shape backgrounds (and safe-area behavior) while propagating background style through view inputs.
• Extends overlay modifiers with style/shape overlays and adds a convenience border implementation.
• Updates GeometryReader UI tests/examples to use shared example views and refreshed snapshot coverage.

Technical Notes: Background/overlay style rendering is now anchored to view bounds and constrained by the current container shape, improving environment propagation to primary content.

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[augmentcode]

Review completed. 2 suggestions posted.

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

[augmentcode]

GeometryProxy.rect(_:in:) returns the input rect unchanged when placementContext is nil, which can make frame(in:) report a local-space rect even when the caller requests a different coordinate space (previously this path returned .zero). Consider handling the nil-context case consistently to avoid silently incorrect frames.

Severity: medium

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[augmentcode]

GeometryProxy.convert(globalPoint:to:) takes a globalPoint but calls transform.convert(.localToSpace(...), point: globalPoint), which looks like an inverted conversion direction for this API and could yield incorrect coordinates. If this is intentional, it might be worth clarifying the expected input space here.

Severity: medium

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[codecov]

Codecov Report

❌ Patch coverage is 0.22676% with 440 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.11%. Comparing base (ec8d089) to head (8178409).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ore/Modifier/ViewModifier/BackgroundModifier.swift	0.00%	211 Missing ⚠️
Sources/OpenSwiftUICore/Shape/ContainerShape.swift	0.00%	127 Missing ⚠️
...wiftUICore/Shape/ShapeStyle/AnchorShapeStyle.swift	0.00%	40 Missing ⚠️
...UICore/Modifier/ViewModifier/OverlayModifier.swift	0.00%	29 Missing ⚠️
...enSwiftUICore/Layout/Geometry/GeometryReader.swift	3.70%	26 Missing ⚠️
...es/OpenSwiftUICore/Layout/View/ViewTransform.swift	0.00%	4 Missing ⚠️
...urces/OpenSwiftUICore/Layout/Geometry/Anchor.swift	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #910      +/-   ##
==========================================
- Coverage   26.35%   26.11%   -0.24%     
==========================================
  Files         710      712       +2     
  Lines       49537    49960     +423     
==========================================
- Hits        13053    13047       -6     
- Misses      36484    36913     +429     

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