fix: accept OpenAPI 3.1 type arrays in networkmock specs

[MaxMichel2]

Summary

• Fix OpenAPI 3.1 spec loading when schema type is an array such as ["string", "null"], accepting both JSON and YAML and keeping the first non-"null" type.
• Accept null entries in schema enums; skip them for generated responses and request-body discriminator matching.
• Add JSON/YAML regression tests reproducing the reported Aruba schema shape, and update KDoc, module documentation, and changelog. No public API signature changes.
• Refresh the tracked Graphify code graph and caches as required by repository guidance; generated graph changes account for most of the diff.

Validation

• Passed: .\gradlew.bat :devview-networkmock-core:testAndroidHostTest "-Pandroidx.baselineprofile.skipgeneration" — 170 tests, including both new regression tests and real sample specs.
• Passed: .\gradlew.bat detektFull; Detekt reported compiler-analysis errors that reduce analysis accuracy.
• Passed: git diff --check and the commit-time Gitleaks hook.
• Not checked: the complete Aruba spec (unavailable locally), iOS compilation, and device tests. Other unsupported OpenAPI 3.1 constructs may still fail.

Scope

Standalone change against main (208e870); no predecessor PR or stack dependency.