feat: add request deduplication for concurrent calls

[DeFex-lab]

Overview

This PR adds a request deduplication layer to the HTTP client so that identical concurrent calls (same method + params) share a single in-flight promise and only trigger one network request. Deduplication is enabled by default and configurable via ClientConfig.

Related Issue

Changes

🔁 Request Deduplication

• [MODIFY] src/http/http-client.ts

  • Added an in-flight request map keyed by method + serialized params.
  • Concurrent callers with identical keys receive the same pending promise.
  • Cache entry is cleared once the response settles (success or failure) so subsequent calls are not deduplicated.

• [MODIFY] src/client.ts

  • Wired deduplication through client methods so all calls go through the shared dedup path.

• [MODIFY] src/config.ts

  • Added deduplication option to ClientConfig (default: enabled).

• [MODIFY] src/__integration-tests__/helpers/mock-http.ts

  • Updated mock HTTP helper to count network requests so deduplication can be asserted.

• [MODIFY] src/http/http-client.test.ts

  • Tests verifying identical concurrent requests resolve to the same response, only one network request is made, and multiple resolvers are satisfied.

Verification Results

npm run lint
✅ No ESLint errors

npm run type-check
✅ No TypeScript errors

npm run test
✅ All tests passing (including new deduplication tests)

npm run build
✅ Successful DTS generation

Acceptance Criteria	Status
Identical concurrent requests return same response	✅ Shared in-flight promise returned to all callers
Only 1 network request made for duplicates	✅ Asserted via mock HTTP request counter
Works across all client methods	✅ Dedup applied at HTTP client layer used by all methods
Configurable deduplication via ClientConfig	✅ deduplication flag added to ClientConfig (default: enabled)
Tests verify single request + multiple resolvers	✅ Added to http-client.test.ts

Closes #119