feat: Add solver HTTP tracing

[bgins]

Summary

This pull request makes the following changes:

• Add solver telemetry config and tracer
• Add gorilla/mux/otelmux middleware to solver HTTP router

The pull request adds OpenTelemetry autoinstrumentation to the solver's HTTP router. It uses our existing tracer provider to send traces to our existing observability infrastructure.

Task/Issue reference

Closes: #387

Test plan

Start the observability stack (https://github.com/Lilypad-Tech/observability) with:

./stack observe-up dev

Start the stack and run a job. Open the observability dashboard at localhost:3000 and run a TraceQL query like:

{resource.service.name="solver" && span.http.method="GET"}

[walkah]

LGTM! Tested locally and I see HTTP traces from the solver ✅