feat: add basic opentelemetry tracing support

[codefromthecrypt]

This adds basic setup for tracing and some tests as a toe-hold. Later pull requests here can enhance the traces with more data. This would be even better if LLM spans were added as discussed here https://github.com/square/exchange/pull/33

Meanwhile, this is what a trace looks like running against ollama using otel-tui as the tracing backend

If any maintainers have any glitch fixes they also have my permission to push directly to this branch.

[codefromthecrypt]

excellent feedback @anuraaga, thanks for dropping by!