Motivation

Copying the overridden Cargo.lock cannot be done as a postUnpack hook because the builder does not cd into the unpacked source until after those hooks are done (thus we effectively end up linking the Cargo.lock to .. when the build runs).

The fix is to change the hook to run later as a prePatch hook

Fixes #422

Checklist

• added tests to verify new behavior
• added an example template or updated an existing one
• updated docs/API.md (or general documentation) with changes
• updated CHANGELOG.md