fix: make perAttemptRecvTimeout actually apply to retry attempts

The perAttemptRecvTimeout field in RetryPolicy has been configurable since
PR #8301 but was never actually applied to individual retry attempts.
The DeadlineEntry in RetriableStream.setDeadline() simply passed through
the original deadline without considering the per-attempt timeout.

Fix: When perAttemptRecvTimeoutNanos is set in the retry policy, apply
the minimum of the original deadline and the per-attempt deadline to
each substream. This ensures that each retry attempt is bounded by the
per-attempt timeout, relative to when the attempt starts.

Fixes #12919

[fj4WqyCCw3C5ShR1RfB7MoBPTpkRrBFYP1uT35g3MvT]

Author: waterWang

core/src/main/java/io/grpc/internal/RetriableStream.java

@@ -754,7 +754,13 @@ public final void setDeadline(final Deadline deadline) {
     class DeadlineEntry implements BufferEntry {
       @Override
       public void runWith(Substream substream) {
-        substream.stream.setDeadline(deadline);
+        if (retryPolicy != null && retryPolicy.perAttemptRecvTimeoutNanos != null) {
+          Deadline perAttemptDeadline =
+              Deadline.after(retryPolicy.perAttemptRecvTimeoutNanos, TimeUnit.NANOSECONDS);
+          substream.stream.setDeadline(deadline.minimum(perAttemptDeadline));
+        } else {
+          substream.stream.setDeadline(deadline);
+        }
       }
     }