fix: preserve requestStream query params

[pragnyanramtha]

Summary

• append HttpRequest.queryParams when building requestStream URLs
• keep the streaming alt=sse default while preserving caller-provided params
• update API client unit coverage for streaming query params and the second-request header assertion

Validation

• npx tsc && cp src/cross/sentencepiece/sentencepiece_model.pb.js dist/src/cross/sentencepiece/ && npx jasmine dist/test/unit/api_client_test.js
• npx eslint src/_api_client.ts test/unit/api_client_test.ts
• npx prettier --check src/_api_client.ts test/unit/api_client_test.ts
• npm run unit-test
• git diff --check