Add task and worker lifecycle metrics to Celery instrumentation

Introduce Flower-compatible metrics for Celery task and worker events:

- flower.events.total: counter for task-sent, task-received,
  task-started, task-succeeded, task-failed, task-retried, task-revoked
- flower.task.runtime.seconds: histogram of task execution time
- flower.worker.number.of.currently.executing.tasks: gauge of in-flight
  tasks per worker
- flower.worker.online: gauge tracking worker online/offline status

CeleryInstrumentor (child process) handles task tracing and task-level
metrics.  CeleryWorkerInstrumentor (main process) handles worker
lifecycle signals (worker_ready, worker_shutdown) and main-process
events (task_received, task_revoked).

Prefetch-time metrics (task_prefetch_time_seconds, worker_prefetched_tasks)
are intentionally omitted — Celery splits task_received and task_prerun
across processes in prefork mode, making it impossible to compute the
delta without external event consumption.

Author: diogosilva30

CHANGELOG.md

@@ -17,6 +17,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4244](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4244))
 - `opentelemetry-instrumentation-sqlite3`: Add uninstrument, error status, suppress, and no-op tests
   ([#4335](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4335))
+- `opentelemetry-instrumentation-celery`: Add task and worker lifecycle metrics matching Celery Flower
+  ([#4439](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4439))
 
 ### Fixed
 
@@ -26,6 +28,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4427](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4427))
 - `opentelemetry-instrumentation-flask`: Clean up environ keys in `_teardown_request` to prevent duplicate execution
   ([#4341](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4341))
+- `opentelemetry-instrumentation-celery`: Fix memory leak in `task_id_to_start_time` dict never being cleaned up
+  ([#4439](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4439))
 
 ### Breaking changes
 

docs/nitpick-exceptions.ini

@@ -48,6 +48,7 @@ py-class=
     fastapi.applications.FastAPI
     starlette.applications.Starlette
     _contextvars.Token
+    celery.worker.request.Request
 
 any=
     ; API

instrumentation/opentelemetry-instrumentation-celery/pyproject.toml

@@ -37,6 +37,7 @@ instruments = [
 
 [project.entry-points.opentelemetry_instrumentor]
 celery = "opentelemetry.instrumentation.celery:CeleryInstrumentor"
+celery_worker = "opentelemetry.instrumentation.celery:CeleryWorkerInstrumentor"
 
 [project.urls]
 Homepage = "https://github.com/open-telemetry/opentelemetry-python-contrib/tree/main/instrumentation/opentelemetry-instrumentation-celery"