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