Add user force orders endpoint

[zaixincheng174-ai]

/claim #88

Closes #88

Summary

• add the signed user force orders endpoint for GET /openApi/swap/v2/trade/forceOrders
• expose it through TradeService and the endpoint barrel export
• add focused unit coverage for service dispatch, request path/method, timestamp serialization, and optional filter omission
• mark the README user force orders feature as supported

Validation

• npx jest src/bingx-client/services/trade-user-force-orders.service.spec.ts --runInBand
• npx eslint src/bingx/endpoints/bingx-user-force-orders-endpoint.ts src/bingx/endpoints/index.ts src/bingx-client/services/trade.service.ts src/bingx-client/services/trade-user-force-orders.service.spec.ts
• npx prettier --check src/bingx/endpoints/bingx-user-force-orders-endpoint.ts src/bingx/endpoints/index.ts src/bingx-client/services/trade.service.ts src/bingx-client/services/trade-user-force-orders.service.spec.ts
• git diff --check
• npm run build

Disclosure

Prepared with AI assistance and locally validated.