fix(schema): recheck external dispatch after resolving - #3705

Summary

resolveExternal can encounter dispatch data created by a nested service call or a concurrent resolver after its initial cache check. Defining the same non-configurable dispatch property again then throws Cannot redefine property.

Check the cache again immediately before each item-level and result-level write, reusing dispatch data already produced while awaiting resolution. This covers repeated result objects and concurrent calls sharing the same array or paginated container.

• Tell us about the problem your pull request is solving.
• Are there any open issues that are related to this? Fixes Cannot redefine property: Symbol(@feathersjs/schema/dispatch) #3476.
• Is this PR dependent on PRs in other repos? No.

Other Information

Added five service-level regressions, all failing with the reported TypeError on the original code. Tests also verify that filtered dispatch data is reused while the original service data remains intact.

npm test --workspace=@feathersjs/schema passes all 42 tests, including compilation and package checks. TypeScript, ESLint, Prettier, and diff checks pass for this change.