Fix/ogc self touch

[NailxSharipov]

Summary

• Fix OGC extraction to split self‑touching contours into shell + holes.

Changes

• Add per‑contour visited mask to isolate edges of a contour.
• Extend OGC test coverage for self‑touch cases.

Testing

• cargo test
• cargo fmt
• cargo clippy

Checklist

• Added tests for new behavior or bug fixes
• Updated docs/examples if needed

[codecov]

Codecov Report

❌ Patch coverage is 89.15663% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
iOverlay/src/core/extract_ogc.rs	90.41%	7 Missing ⚠️
iOverlay/src/core/extract.rs	80.00%	2 Missing ⚠️

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