bench: add StyleX Turbopack benchmark

[owjs3901]

Summary

• update the StyleX Turbopack benchmark to the official StyleX 0.19 Babel and PostCSS integration
• add a StyleX Turbopack benchmark where Devup UI alone extracts StyleX styles
• include both benchmarks in bun benchmark

Closes #643

Validation

• bun run --filter next-stylex-turbo-benchmark build

The StyleX-only production build completed with Turbopack and emitted the expected StyleX CSS.

The Devup UI comparison app could not be built locally because the environment blocks wasm-pack.exe via application control; it requires the repository WASM package to be built first.

[github-actions]

Changepacks

[codecov]

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