fix: limit .mbtp inputs to check and prove

[peter-jerry-ye]

Summary

Proof helper files were unconditionally copied into every build target projection, so commands such as moon test passed them to moonc even though only moon check and moon prove should consume them.

This change gates .mbtp projection on the Check and Prove run modes while leaving package discovery and metadata unchanged. The existing verification fixture now asserts that check and prove include the helper, while build, test, bench, and bundle do not.

The change is limited to target file selection and its regression coverage.

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
crates/moon/tests/test_cases/moon_prove/mod.rs	0% smaller
crates/moonbuild-rupes-recta/src/build_plan/builders.rs	0% smaller