fix: correct lazy compilation backend options schema

[chenjiahan]

Summary

The zod schema for the lazyCompilation.backend configuration is out of date and this PR updates the schema to match with the type declaration.

See: https://rspack.dev/config/experiments#experimentslazycompilation

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

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[codspeed-hq]

CodSpeed Performance Report

Merging #9138 will not alter performance

_{Comparing lazy_compilation_schema_0129 (8985de0) with main (cc5e3f6)}

Summary

✅ 6 untouched benchmarks