Fix grid-area span reset for overriding areas

[puneetdixit200]

Summary

• Emit -ms-grid-*-span: 1 when a later grid-area rule can overlap an earlier area with a larger span.
• Add regression coverage for overriding a broad grid-area assignment with narrower child rules.

Tests

• node node_modules\\uvu\\bin.js test
• npx --yes pnpm@10.26.0 run test:lint
• npx --yes pnpm@10.26.0 run test:size
• npx --yes pnpm@10.26.0 exec c8 node node_modules\\uvu\\bin.js test
• git diff --check

Fixes #1292