Add oneOf tests in composed test spec for TS

[wing328]

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Summary by cubic

Add oneOf coverage to TypeScript test specs and regenerate sample clients. Also fix typescript-fetch oneOf array handling and configure the sample for npm publishing.

• New Features
  • Added OneOfPrimitiveTypes.value to composed-schemas.yaml and typescript-fetch/oneOf.yaml with oneOf: boolean, int64, PetByAge/TestA, and arrays of those models.
  • Regenerated TypeScript clients (typescript, typescript-axios, typescript-fetch) and updated serializers/exports to include OneOfPrimitiveTypes and OneOfPrimitiveTypesValue.
  • Configured typescript-fetch sample with npm metadata and packaging (npmName/version/repo, README, package.json, tsconfig) and updated docs/imports to use @openapitools/typescript-fetch-petstore.

^{Written for commit 461c5d1. Summary will update on new commits.}