Avoid having shared mutable state between JsonSchema invocations

[OptimumCode]

Instead of having a shared reference resolver we now create a new one for each validate method invocation. This removes the shared mutable state when JsonSchema is invoked from multiple threads.

This change should not affect performance much as the reference resolver is created only once per validate method invocation.

Resolves #224

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.53%. Comparing base (65960ab) to head (ae3f0c8).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #226   +/-   ##
=======================================
  Coverage   90.52%   90.53%           
=======================================
  Files         133      133           
  Lines        3980     3983    +3     
  Branches     1059     1059           
=======================================
+ Hits         3603     3606    +3     
  Misses         82       82           
  Partials      295      295           

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[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'KMP JSON schema validator'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.50.

Benchmark suite	Current: ae3f0c8	Previous: 65960ab	Ratio
macosArm64.CommonAvgTimeBench.validateDetailed ( {"objectPath":"openapi-invalid.json","schemaPath":"openapi_schema.json"} )	4195.897892397661 us/op	2633.6733204188486 us/op	1.59
macosArm64.CommonAvgTimeBench.validateFlag ( {"objectPath":"openapi.json","schemaPath":"openapi_schema.json"} )	1130.3611502570693 us/op	732.0572680586081 us/op	1.54

This comment was automatically generated by workflow using github-action-benchmark.

CC: @OptimumCode