feat: add OTLP export into tracing setup with context propagation helpers

[adarsh0728]

What this PR does / why we need it

• This PR introduces dependencies, context propagation helpers, and OTLP exporter wiring. No behavioral change unless OTEL_EXPORTER_OTLP_ENDPOINT env var is set.
• OTEL_TRACES_SAMPLER && OTEL_TRACES_SAMPLER_ARG can be configured for sampling

Related issues

Fixes #3378

Testing

Deploy with OTEL_EXPORTER_OTLP_ENDPOINT pointed at Jaeger — verified there are no crashes, exporter connects

[setup_tracing] Configuring OTLP exporter: endpoint=http://simplest-jaeger-collector.default:4317, service_name=numaflow-test
[setup_tracing] Sampler: parentbased_traceidratio, ratio=0.01
[setup_tracing] OTLP tracing ENABLED

{"timestamp":"2026-04-20T14:02:25.475288Z","level":"INFO","message":"Forwarder is starting...","target":"numaflow_core::monovertex"}
{"timestamp":"2026-04-20T14:02:25.475536Z","level":"INFO","message":"Started streaming source with batch size","self.read_batch_size":"500","target":"numaflow_core::source"}
{"timestamp":"2026-04-20T14:02:25.475982Z","level":"INFO","message":"Starting sink writer","self.batch_size":"500","self.chunk_timeout":"1s","target":"numaflow_core::sinker::sink"}
{"timestamp":"2026-04-20T14:02:26.471891Z","level":"INFO","message":"Processed messages per second","processed":"81500","target":"numaflow_core::tracker"}
{"timestamp":"2026-04-20T14:02:27.471820Z","level":"INFO","message":"Processed messages per second","processed":"82500","target":"numaflow_core::tracker"}

• No drop / queue full / BatchSpan warnings — the span-only filter is working

Spec used

apiVersion: numaflow.numaproj.io/v1alpha1
kind: MonoVertex
metadata:
  name: simple-mono-vertex
spec:
  source:
    udsource:
      container:
        image: quay.io/numaio/numaflow-rs/simple-source:stable
    transformer:
      container:
        image: quay.io/numaio/numaflow-rs/source-transformer-now:stable
  udf:
    container:
      image: quay.io/numaio/numaflow-go/map-cat:stable
      imagePullPolicy: IfNotPresent
  sink:
    udsink:
      container:
        image: quay.io/numaio/numaflow-rs/sink-log:stable
  containerTemplate:
    env:
      - name: OTEL_EXPORTER_OTLP_ENDPOINT
        value: "http://simplest-jaeger-collector.default:4317"
      - name: OTEL_SERVICE_NAME
        value: "numaflow-test"
      - name: OTEL_TRACES_SAMPLER
        value: "parentbased_traceidratio"
      - name: OTEL_TRACES_SAMPLER_ARG
        value: "0.01"

Special notes for reviewers

• Tokio runtime created before tracing init (required for tonic gRPC exporter)

[codecov]

Codecov Report

❌ Patch coverage is 82.18924% with 96 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.23%. Comparing base (06440fc) to head (db894d3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
rust/numaflow/src/setup_tracing.rs	72.24%	63 Missing ⚠️
rust/numaflow/src/main.rs	0.00%	26 Missing ⚠️
rust/numaflow-core/src/shared.rs	0.00%	4 Missing ⚠️
rust/numaflow-core/src/shared/otel.rs	98.93%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3385      +/-   ##
==========================================
- Coverage   82.55%   81.23%   -1.33%     
==========================================
  Files         306      307       +1     
  Lines       74445    78064    +3619     
==========================================
+ Hits        61460    63415    +1955     
- Misses      12427    14094    +1667     
+ Partials      558      555       -3     

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[adarsh0728]

Opentelemetry's general recommendation is to have sampling if we generate more than 1000 traces per second.
Currently, head sampling is implemented based on the env variables which user can configure OTEL_TRACES_SAMPLER and OTEL_TRACES_SAMPLER_ARG depending on their throughput.

azure sdk example

[vigith]

I have pushed some changes, please review, and feel free to revert it. I made "a change" per commit.

Could you please improve the test coverage?