feat: OTEL semantic convention compliance and req/resp metrics

[prestwich]

this PR is really cool:

• add service name to router, defaulting to ajj
• comply with OTEL semantic conventions (see exception in README)
• axum router now propagates traceparent details to the span :)
• add metrics for requests received, processed, succeeded, errors, and responses sent/omitted
• metric labels by service name and method
• improve tracing span propagation to include more request lifecycle within the request span
• delegate handler implementation to a macro to DRY it as much as possible
• Simplify ResponsePayload by making a transparent wrapper around Result

[prestwich]

• feat: ipc and axum serving example #33
• feat: OTEL semantic convention compliance and req/resp metrics #32 👈 (View in Graphite)
• main

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