Add release schema validation

[theory]

Rewrite bulid.rs to simply write each schema file on a single line instead of building up a merge structure. This allows each schema to be fetched from the compiler, rather than just distribution.schema.json. It's simpler, too.

Then update the compiler package to load each line into the compiler. This requires splitting the compiled-in schema_v1 and schema_v2 strings into lines, but it works just fine.

Add a new method to the valid package, validate_release, that validates a META.json file that includes release metadata. Since the functionality is identical to the existing validate method, aside from the schema name, refactor it into the new validate_schema method, now simply dispatched by both validate and validate_release.

Expand the corpus test to test both validate and validate_release by applying a patch containing valid release metadata. While there, add tests for the return values, to ensure that the correct verision is always returned from both methods.

Finally, eliminate some redundant tests and test the string values of errors, then add tests for validation failures for both validate and validate_release.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (f1650e5) to head (426128a).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #27   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          886       887    +1     
=========================================
+ Hits           886       887    +1     

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