chore: mark compiler.compile as private method

[chenjiahan]

Summary

compiler.compile is an internal low-level method and should not be used by Rspack users.

This PR removes compiler.compile from the documentation and marks it as @private.

Checklist

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

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[codspeed-hq]

CodSpeed Performance Report

Merging #9472 will not alter performance

_{Comparing compile_method_0226 (2635310) with main (912f2b3)}

Summary

✅ 7 untouched benchmarks