[#144] Rename semver test functions and checkoutLockedVersions

[bguidolim]

Summary

• Rename test functions from semver* to versionCompare* to match the VersionCompare type (renamed from SemVer in [#144] Remove pack version field and peer dependency system #179)
• Rename checkoutLockedVersions to checkoutLockedCommits for consistency with commit-based pinning

Test plan

• swift build compiles cleanly
• swift build --build-tests compiles cleanly

[Copilot]

Pull request overview

Renames remaining “semver” and “locked versions” identifiers to align with the newer VersionCompare naming and commit-SHA-based locking semantics introduced in #179.

Changes:

• Rename ExternalPackLoaderTests test functions from semver* → versionCompare*.
• Rename LockfileOperations.checkoutLockedVersions → checkoutLockedCommits.
• Update SyncCommand’s --lock flow to call the renamed method and adjust the nearby comment wording.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
Tests/MCSTests/ExternalPackLoaderTests.swift	Renames VersionCompare-related test function identifiers for consistency with the VersionCompare type.
Sources/mcs/Install/LockfileOperations.swift	Renames the lockfile checkout helper to reflect commit-based pinning.
Sources/mcs/Commands/SyncCommand.swift	Updates --lock call site and comment to use “commits” wording and the new method name.

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