All tests for the current semispace have passed. I've rebased to the draft pull request.
 Changes:
- I implemented process_weak_refs which is invoked by a workbucket to process weak references.
  Internally, it uses jtoc_call to reuse existing JikesRVM methods.

changes:
  - Refactor to use state machine style scanning
  - Remove unnecessary debugging code

- Fix style-check
- Upgrade heap size in weak-ref and normal test
- Disable flaky test

* Add a new configuration setting. The test script has been updated to modify this configuration using `sed`.
* Employ Rust's `cfg` attribute to conditionally compile specific modules/functions.