Emit ActivityTaskFailedCounter for canceled activities

Problem:
Customer reported cadence-activity-task-failed metric not emitted when
activities fail due to heartbeat timeout. Root cause is context.Canceled
errors convert to RespondActivityTaskCanceledRequest, which only emits
ActivityTaskCanceledCounter.

Solution:
Modified reportActivityComplete() and reportActivityCompleteByID() to emit
both ActivityTaskCanceledCounter and ActivityTaskFailedCounter when
activities are canceled. Cancellations from timeouts are failures from a
monitoring perspective.

Changes:
- internal/internal_task_pollers.go: Added ActivityTaskFailedCounter.Inc(1)
  in canceled case for both functions

Testing:
- go build ./internal/... - compiles successfully
- go test ./internal - all existing tests pass
- go test ./internal/common/metrics - metrics infrastructure verified
- Verified ActivityTaskFailedCounter already defined and used for explicit
  failures (line 71 constants.go, line 1296 internal_task_pollers.go)

Backward compatible. No breaking changes to server communication.

Signed-off-by: Diana Zawadzki <[email protected]>
Signed-off-by: Diana Zawadzki <[email protected]>

Author: zawadzkidiana

internal/internal_task_pollers.go

@@ -1289,6 +1289,9 @@ func reportActivityComplete(
 		switch request.(type) {
 		case *s.RespondActivityTaskCanceledRequest:
 			metricsScope.Counter(metrics.ActivityTaskCanceledCounter).Inc(1)
+			// Also emit failed counter for canceled activities since they represent failures
+			// from a customer monitoring perspective (e.g., heartbeat timeouts)
+			metricsScope.Counter(metrics.ActivityTaskFailedCounter).Inc(1)
 		case *s.RespondActivityTaskFailedRequest:
 			metricsScope.Counter(metrics.ActivityTaskFailedCounter).Inc(1)
 		case *s.RespondActivityTaskCompletedRequest:
@@ -1342,6 +1345,9 @@ func reportActivityCompleteByID(
 		switch request.(type) {
 		case *s.RespondActivityTaskCanceledByIDRequest:
 			metricsScope.Counter(metrics.ActivityTaskCanceledByIDCounter).Inc(1)
+			// Also emit failed counter for canceled activities since they represent failures
+			// from a customer monitoring perspective (e.g., heartbeat timeouts)
+			metricsScope.Counter(metrics.ActivityTaskFailedByIDCounter).Inc(1)
 		case *s.RespondActivityTaskFailedByIDRequest:
 			metricsScope.Counter(metrics.ActivityTaskFailedByIDCounter).Inc(1)
 		case *s.RespondActivityTaskCompletedByIDRequest: