test: add functional test for new cluster mempool RPCs

Co-authored-by: glozow <gloriajzhao@gmail.com>

test/functional/test_framework/mempool_util.py

@@ -33,6 +33,8 @@ from .wallet import (
 DEFAULT_MIN_RELAY_TX_FEE = 100
 # Default for -incrementalrelayfee in sat/kvB
 DEFAULT_INCREMENTAL_RELAY_FEE = 100
+DEFAULT_CLUSTER_LIMIT = 64
+DEFAULT_CLUSTER_SIZE_LIMIT_KVB = 101
 
 TRUC_MAX_VSIZE = 10000
 TRUC_CHILD_MAX_VSIZE = 1000