Add prometheus metics format to worker

[Uche44]

Successfully added Prometheus text-based exposition format support to the stream processing worker's metrics endpoint.

• Closes issue obs: Add Prometheus metrics format to worker #226

##Changes Made
###Stream Processing Worker (xstreamroll-processing)

• metrics.ts

Updated startMetricsServer to route metric requests to either Prometheus format or JSON based on the URL path (/metrics, /metrics/json, /metrics/prometheus) and the Accept header.

Implemented content negotiation: If the client requests /metrics with Accept: application/json (excluding standard browser wildcard accepts or text/plain), it returns JSON. Otherwise, it defaults to standard Prometheus formatting.

Added # HELP and # TYPE comments to the Prometheus exposition format output.

• metrics.test.ts

Added a full suite of integration tests for the metrics server.

Used port 0 for test server instantiation to dynamically allocate a free port on the host, avoiding port collisions.

Covered all permutations of request routing, content negotiation headers (Accept), and default response types.

Verification Results
Automated Tests
Ran the full test suite in xstreamroll-processing successfully:

[Uche44]

@Xhristin3 please merge

[Xhristin3]

Nice work on this one @Uche44! The content negotiation logic is clean — love how you handled the Accept header edge cases (excluding */* and text/plain from triggering JSON). The Prometheus exposition format includes proper # HELP and # TYPE comments, and the test suite covers all the endpoint permutations + 404 routing. Really thorough. Closes #226 cleanly. 🚀

[Uche44]

Thank you @Xhristin3