WIP: Group mega fixtures to reduce build calls

[matthewp]

Summary

• consolidate moved fixtures into grouped mega-static/mega-frameworks test files
• reduce repeated fixture.build() calls by sharing builds per config
• add per-group outDir/cacheDir to avoid dist and Vite cache collisions
• WIP: this is a test to reduce the number of fixtures and evaluate CI time impact

Testing

• node packages/astro/test/mega-frameworks-0-css.test.js
• node packages/astro/test/mega-static-core.test.js
• node packages/astro/test/mega-static-site-base.test.js
• node packages/astro/test/mega-static-ssr.test.js

[changeset-bot]

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Latest commit: 10ace07

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