chore: improve RhythmBlocks branch coverage [#5607]

[Mohd-Ali-Creator]

Improves branch coverage for RhythmBlocks.js by adding
tests for previously uncovered paths.

Coverage improvement:

• Statements: 66.22% → 73.11%
• Branches: 54.28% → 58.09%
• Lines: 72.62% → 80.29%

New tests added:

• NoteBlock callback queue path (lines 193-197)
• SwingBlock listener suppressOutput paths (lines 253-258)
• NewSwingBlock flow and listener paths (lines 307-328)

All 35 tests passing ✅
Full suite: 4004/4004 green ✅

PR Category

• Bug Fix - Fixes a bug or incorrect behavior
• Feature - Adds new functionality
• Performance - Improves performance
• Tests - Adds or updates test coverage
• Documentation - Updates to docs, comments, or README

[github-actions]

This PR has merge conflicts with master.

Please rebase your branch:

# Add upstream remote (one-time setup)
git remote add upstream https://github.com/sugarlabs/musicblocks.git

# Fetch latest master and rebase
git fetch upstream
git rebase upstream/master

# Resolve any conflicts, then:
git push --force-with-lease origin YOUR_BRANCH

Tip: Enable "Allow edits from maintainers" on this PR so we can auto-rebase for you next time. This only grants access to your PR branch. Your fork's other branches are not affected.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

Coverage: Coverage summary unavailable

[github-actions]

Merge conflicts resolved. Ready for review.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

Coverage: Statements: 42.45% | Branches: 34.99% | Functions: 46.56% | Lines: 42.87%

[Mohd-Ali-Creator]

Hi @vyagh @walterbender,

PR #6738 improves RhythmBlocks.js branch coverage.

Coverage improvement:

• Statements: 66% → 73%
• Branches: 54% → 58%
• Lines: 72% → 80%

All 10 CI checks passing ✅

Could you please take a look when you get a chance? 🙏

[walterbender]

Did you do a rebase before making this commit? It seems like lots of unrelated changes in the commit.

[Mohd-Ali-Creator]

Hi @walterbender,

Apologies for the confusion! The previous commit
had unintended deletions due to a rebase conflict
resolution error.

Fixed: restored all upstream tests and added only
my new coverage tests on top.

Now: 65 tests passing, no deletions of existing tests.

Sorry for the trouble! 🙏

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

Coverage: Statements: 42.55% | Branches: 35.13% | Functions: 46.72% | Lines: 42.96%