fix(atenet): propagate trace context through router and namespace span/metric attrs

[SURAJ KUMAR (krsnaSuraj)]

Fixes #427

Root cause

Two bugs broke the trace chain through the router, creating two separate traces instead of one connected trace for each ResumeActor request:

1. Singleflight detaches trace context (primary)

resumer.go:58 uses context.Background() inside singleflight.DoChan(). The otelgrpc client handler reads the trace context from the context passed to the gRPC call, so the ateapi handler spans ended up in a separate trace from the router's ResumeActor span.

Fix: Propagate the caller's span context into the background context via trace.ContextWithSpanContext. The caller's lifecycle detachment is preserved (background context parent), but the trace chain is maintained.

2. No traceparent injected into upstream request (secondary)

extproc.go:179-187 only rewrote the :authority header in the HeadersResponse mutation. When Envoy tracing is not configured (no OTLP collector), Envoy does not inject traceparent into upstream requests, so the worker pod receives no trace context.

Fix: After building the header mutation, call injectTraceContext(ctx, mutation) which uses otel.GetTextMapPropagator().Inject() to write traceparent/tracestate into the mutation set headers.

3. Non-namespaced attribute keys

Span and metric attributes used bare keys (atespace, actor, actor_template_namespace, etc.) instead of the ate.* namespaced convention established in #412.

Fix: Renamed attributes across extproc.go and resumer.go:

• atespace -> ate.atespace
• actor -> ate.actor_name
• target_addr (new) -> ate.target_addr
• actor_template_namespace -> ate.actor_template_namespace
• actor_template_name -> ate.actor_template_name
• outcome -> ate.outcome

Also added missing ate.atespace and ate.actor_name attributes to the ExtProc.RequestHeaders span (previously had zero custom attributes).

Testing

• Existing TestExtProcHeadersEvaluation updated to handle additional trace headers in the mutation (searches for :authority among SetHeaders instead of asserting exactly one entry).
• TestHandleRequestHeadersDoesNotLogSensitiveData unaffected (no mutation assertion).
• TestActorResumer_ResumeActor unaffected (tests the resumed actor, not span internals).

fix(atenet): connect router traces across ateapi, atelet, and worker by propagating span context through singleflight and injecting traceparent into ext_proc mutations; namespace all span and metric attributes to ate.*

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