fix: Load schema with fetch, default to JSR package

[effigies]

The current version emits a more-or-less obligatory error due to the use of import with an https URL. That seems like a thing of Deno past.

Given that we're hosting the schema at the JSR, let's go ahead and default to that. If someone wants to provide a URL, then a fetch can be done and the JSON can be loaded. This means BIDS_SCHEMA pointing to local files will need to use file:///..., but that seems fine.

[codecov]

Codecov Report

Attention: Patch coverage is 22.22222% with 14 lines in your changes missing coverage. Please review.

Project coverage is 87.58%. Comparing base (b087c35) to head (0d12f90).
Report is 3 commits behind head on master.

Files	Patch %	Lines
bids-validator/src/setup/loadSchema.ts	22.22%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2112      +/-   ##
==========================================
+ Coverage   85.69%   87.58%   +1.88%     
==========================================
  Files          91      133      +42     
  Lines        3782     6973    +3191     
  Branches     1220     1656     +436     
==========================================
+ Hits         3241     6107    +2866     
- Misses        455      771     +316     
- Partials       86       95       +9     

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[effigies]

@nellh Just pushed a commit to remove a default value from the --schema CLI flag, squeezed in after your review.