feat(otel): optional OpenTelemetry tracing (ADR-0025)

[muhammetsafak]

The PHP mirror of babelqueue-go/otel / babelqueue.otel / @babelqueue/core/otel (ADR-0025): optional OpenTelemetry tracing as a new BabelQueue\Otel\Tracing, with open-telemetry/api as an optional suggest dependency — so the core stays dependency-light (GR-7).

What

• traceIdOf/uuidOf — trace_id (a UUID) ↔ 32-hex OTel TraceId (otherwise SHA-256). The already-propagated trace_id becomes the shared OTel trace across every hop/SDK — no envelope change (GR-1).
• Tracing::wrap($tracer, $handler) — a CONSUMER span process <urn> in the trace_id-derived trace, with messaging-semconv attributes + error recording. Mirrors the SchemaValidated::wrap / Idempotent::wrap shape and composes with the ack-on-return / redeliver-on-throw contract.
• Tracing::publish($tracer, $transport, $urn, $data) — a PRODUCER span publish <urn> that builds the envelope with the active trace's id as trace_id, encodes and publishes through the Transport.

Tests / gates

• tests/Otel/TracingTest.php (7 tests) against the OTel SDK in-memory exporter. Full suite: 160 tests green; PHPStan level 9 clean. open-telemetry/api + open-telemetry/sdk added to require-dev; open-telemetry/api to suggest.

Honest limit

One correlated trace per trace_id; exact cross-hop span parent-child (W3C traceparent as a transport header) is the documented follow-up.

🤖 Generated with Claude Code