feat(indexer): document GraphQLIndexer.query return contract and add generic return typing (closes #599)

[Ranjeet2063]

Summary

Documents the unwrapped data return contract of GraphQLIndexer.query() and equips the method with strongly-typed generic return support query<T = unknown>(): Promise<T> (closes #599).

Changes

• src/indexer.ts:
  • Updated query method signature to async query<T = unknown>(options: GraphQLQueryOptions): Promise<T> and cast return payload to T.
  • Added comprehensive JSDoc detailing the unwrapped return contract (body.data vs { data, errors } envelope) and usage examples with TypeScript interfaces.
• docs/api.md:
  • Documented ### query<T = unknown>(options) → Promise<T> with a prominent note clarifying the unwrapped body.data payload and generic typing.
• src/tests/graphql-indexer-query-return-contract.test.ts:
  • Added 4 unit tests verifying unwrapped payload delivery, generic type parameter propagation, null payload handling, ConduitError on GraphQL error responses, and APQ hash miss retry unwrapping.

Verification

• 16/16 unit tests passing across indexer test suites.
• Clean TypeScript compilation (tsc --noEmit).
• Zero ESLint errors.
• Successful ESM and CJS production Rollup builds.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.