Switch to typescript 7, remove tsdown

[hildjj]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.47%. Comparing base (f821aad) to head (fedd49b).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #29      +/-   ##
==========================================
- Coverage   99.68%   99.47%   -0.22%     
==========================================
  Files           5        5              
  Lines         951      951              
  Branches       79       87       +8     
==========================================
- Hits          948      946       -2     
- Misses          3        5       +2     

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[hildjj]

Coverage change is due to differences in sourcemapping I think.