#24941 Add typescript-fetch sample to test temporal (dateLibrary option)

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Summary by cubic

Adds a typescript-fetch sample build configured with dateLibrary: temporal so the Temporal date support has checked-in sample coverage, and bumps the shared typecheck script to TypeScript 6.0.3.

• Uses the date-handling.yaml spec, which covers date and date-time values in paths, query parameters, form parameters, models, and a oneOf.
• Adds the generated client under samples/client/petstore/typescript-fetch/builds/date-library-temporal with npm packaging enabled; no generator behavior changes.
• Bumps bin/ts-typecheck-all.sh to TypeScript 6.0.3 to typecheck the generated samples.