feat: Propagate process context to profiles

[nsavoire]

Summary

Propagate OTel ProcessContext resource attributes (per OTEP #4719) to the OTLP profile output so profiles can be correlated with the rest of the telemetry from the same service instance.

Changes

processcontext:

• Info.Resource is now a *pcommon.Resource (was *resourcepb.Resource), so resource attributes flow directly into the OTLP reporter without re-conversion. convertAnyValue handles all AnyValue variants including
  nested arrays/maps.
• WithMergedEnvVars(info, envVars) enriches an Info with OTEL_SERVICE_NAME and OTEL_RESOURCE_ATTRIBUTES. Per the OTel resource SDK spec: keys and values are percent-encoded; on any decoding error the entire OTEL_RESOURCE_ATTRIBUTES value is discarded; duplicate keys within it resolve last-writer-wins; OTEL_SERVICE_NAME overrides service.name if both are set; values from the proto resource win over env-var-derived ones on collision.
• ResourceToContextKey(resource) returns a stable key from the (service.namespace, service.name, service.instance.id) triplet — described as globally unique by the semantic conventions. Used in ResourceKey for trace deduplication grouping.
• Info is documented as immutable after publication; the embedded *pcommon.Resource is shared by pointer across the process-manager writer, the tracer event loop, and the reporter, and must be treated as read-only by all holders.

processmanager:

• SynchronizeProcess defers the processcontext.Read until after GetProcessMeta, so env vars are available to merge in the same sync. readProcessContext returns (Info, publish bool): false preserves the previously-published context on transient ErrNoUpdate/ErrConcurrentUpdate, true publishes a new context.

Behaviour notes

• Processes without an OTEL_CTX mapping are unchanged: Info.Resource stays nil, ContextKey == NullString, and bucketing falls back to the existing PID/container/executable keys.
• Env-var-only fallback: a process that sets OTEL_SERVICE_NAME / OTEL_RESOURCE_ATTRIBUTES but doesn't publish a ProcessContext mapping still gets a Resource derived from those env vars.
• setResourceAttributes copies the process context attributes onto the emitted ResourceProfiles. eBPF-derived process.pid, container.id, and process.executable.* are added on top. APMServiceName, when set, takes precedence over the process context supplied service.name. This override is transitional and APMServiceName should be removed once ProcessContext is the canonical source of service identity.

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