Adjust visibility of codependent MutableRepo and CommitBuilder functions #9533

Job	Run time
Check protos	23s
build (ubuntu-latest)	3m 15s
Check formatting	18s
Check that MkDocs can build the docs with Poetry 1.3.2	35s
build (macos-14)	2m 33s
build (windows-latest)	7m 5s
build (ubuntu-latest, --all-features)	4m 5s
cargo-deny (advisories)	26s
cargo-deny (bans licenses sources)	28s
Clippy check	2m 20s
Check that MkDocs can build the docs	22s
	21m 50s

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