DatastoreStorage.apply_commit: set NDB transaction retries to 10

retry aggressively because repo writes can be bursty and cause high
contention. (ndb does exponential backoff.)

https://console.cloud.google.com/errors/detail/CKbL5KSX98uZHw;time=P1D;locations=global?project=bridgy-federated

arroba/datastore_storage.py

@@ -569,7 +569,10 @@ def write(self, repo_did, obj, seq=None):
         return AtpBlock.create(repo_did=repo_did, data=obj, seq=seq).to_block()
 
     @ndb_context
-    @ndb.transactional()
+    # retry aggressively because repo writes can be bursty and cause high
+    # contention. (ndb does exponential backoff.)
+    # https://console.cloud.google.com/errors/detail/CKbL5KSX98uZHw;time=P1D;locations=global?project=bridgy-federated
+    @ndb.transactional(retries=10)
     def apply_commit(self, commit_data):
         commit = commit_data.commit.decoded
         if repo := AtpRepo.get_by_id(commit['did']):