Clean up CSS HMR invalidation tests

[thelazylamaGit]

This PR targets astro-bot’s branch for #16783 and applies the requested CI/test clean up + a small dev-server regression test for the actual stale inline CSS behaviour. It does not change the fix implementation.

Changes

• Adds idToModuleMap: new Map() to the existing hmr-reload.test.ts mock so it matches the new module graph iteration added in Fix stale inline CSS in server-rendered HTML during dev #16783.
• Replaces the unsafe Function cast in hmr-css-invalidation.test.ts with a local typed hot update handler helper.
• Adds a minimal dev-server fixture test that requests a getStaticPaths() route, edits global CSS, then verifies the next SSR response contains updated inline CSS.
• Keeps the main CSS HMR invalidation implementation unchanged.

Testing

• Fixes the current Test (astro) failure caused by the mocked environment.moduleGraph missing idToModuleMap.
• Fixes the lint/type failure from @typescript-eslint/no-unsafe-function-type.
• Keeps unit coverage for virtual:astro:dev-css:* module graph invalidation.
• Adds integration-style coverage for the actual stale SSR inline CSS behavior using Astro’s dev server, fixture.fetch(), and fixture.editFile().

Docs

No docs changes needed. This only fixes internal dev-server HMR cache invalidation behavior and test coverage.

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Latest commit: eb5b07d

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