Bump the project version from 0.5.3 to 0.5.4 and update the crucible_ir
dependency requirement to 0.2.1.

Changes:
- Increment version to 0.5.4 in mix.exs
- Update crucible_ir dependency to 0.2.1 in mix.exs
- Update mix.lock to track the new dependency version
- Update installation instructions in README.md to reflect the new version
- Add 0.5.4 release entry to CHANGELOG.md documenting the dependency change