Sibling of OpenTelemetryMiddleware, wired on the same Messenger bus via
OpenTelemetryExtension::prepend() when metrics.messenger.enabled. Dispatch
side is out of scope for this first metrics drop; emission triggers on
ReceivedStamp or ConsumedByWorkerStamp presence.

Metrics (OTel messaging metrics semconv, Development status as of 2026-04):
- messaging.process.duration             (Histogram, unit 's')
- messaging.client.consumed.messages     (Counter,  unit '{message}')

Attributes on every emission:
- messaging.system                  (required)    = 'symfony_messenger'
- messaging.operation.name          (required)    = 'process'
- messaging.operation.type          (trace-compat) = 'process'
- messaging.destination.name        (conditional) = ReceivedStamp::getTransportName()
- error.type                        (conditional, on failure) = short exception class

Mirrors the tracer subscriber pattern: each subscriber owns its Meter
lazy-resolved from Globals::meterProvider(), caches instruments locally,
implements ResetInterface to clear everything between worker iterations.
No cross-subscriber dependency. Same shape as ConsoleSubscriber uses for
the tracer today, so upcoming HTTP/Doctrine/Cache metric subscribers
can follow the same form.

Metric name resolution is centralized in a private method, ready for
OTEL_SEMCONV_STABILITY_OPT_IN dual-emit once messaging metrics stabilize.

Config validation rejects metrics.messenger.enabled without metrics.enabled.

Refs tracewayapp#21

Extends OTelTestTrait with an in-memory MeterProvider + ExportingReader so
any test can assert on emitted metrics via collectMetrics().

Coverage:
- MeterRegistry: instrument caching per name, emitted values/attributes,
  reset behavior.
- OpenTelemetryMetricsMiddleware: counter + histogram emission on consume,
  semantic convention attributes (including required messaging.operation.name),
  error.type on failure, queue exclusion, dispatch-side passthrough, reset
  clears cached meter and instruments, ConsumedByWorkerStamp without
  ReceivedStamp omits destination attribute.
- BundleBootTest: metrics services correctly wired based on nested config,
  validation rejects metrics.messenger.enabled without metrics.enabled.

Refs tracewayapp#21

Adds a Metrics section to the README covering:
- nested config tree (metrics.enabled, metrics.meter_name,
  metrics.messenger.enabled, metrics.messenger.excluded_queues)
- note that the nested shape is a forward-compatible choice for the
  planned v2 config rework, not an inconsistency with the 1.x flat keys
- emitted instruments table with OTel semantic convention attributes
  (messaging.process.duration + messaging.client.consumed.messages)
- explicit note on semconv status: all messaging metrics and attributes
  are currently Development in the spec; only error.type is Stable
- scope note: excluded_queues is consume-side only (ReceivedStamp), and
  dispatch-side metrics are out of scope for this first drop
- MeterRegistryInterface injection example for custom business metrics
- OTEL_METRICS_EXPORTER and OTEL_EXPORTER_OTLP_METRICS_ENDPOINT env vars

Refs tracewayapp#21

…s.duration

The OTel SDK defaults are tuned for milliseconds and collapse all
sub-5s jobs into the first bucket, making p95/p99 unusable. The new
boundaries mirror the HTTP semconv recommendation for second-based
durations.

Wrap record() in a try/finally with a swallowing catch so that a broken
metric provider, exporter or instrument cannot replace the original
business exception with a metric error.