Replace rollup with rolldown

[birkskyum]

POC of what migration to rolldown bundling will look like - so we have that option for later when it's stable and more widely adopted.

It seems like it's already compatible at this time, and able to pass the test suite. In this PR i've focused on keeping the git diff minimal (thus not renamed rollup.config -> rolldown.config etc.)

Rollup plugins for json and commonjs aren't needed with rolldown AFAICT.

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Post benchmark scores.
• Add an entry to CHANGELOG.md under the ## main section.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.18%. Comparing base (31ae5f8) to head (1a8d7d5).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1132      +/-   ##
==========================================
- Coverage   95.18%   95.18%   -0.01%     
==========================================
  Files         114      114              
  Lines        7359     7358       -1     
  Branches     2318     2318              
==========================================
- Hits         7005     7004       -1     
  Misses        354      354              

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[HarelM]

@birkskyum where are we with this PR? Should it be closed or pushed forward?

[birkskyum]

It's still relevant, and apart from a version bump i don't expect other changes.

Rolldown is moving towards stabilization very fast, and adoption is growing quickly too, even on the beta versions before it'll be auto-updated by many times more:

I think already now, for such a simple repo as we have here, it's probably fine, but it'll be stable in 1-2 months, so we might as well just wait for that.