test: utxocache:* tracepoint tests

This adds tests for the
- utxocache:flush
- utxocache:uncache
- utxocache:add
- utxocache:spent
tracepoint interfaces.

test/functional/test_runner.py

@@ -169,6 +169,7 @@ BASE_SCRIPTS = [
     'interface_http.py',
     'interface_rpc.py',
     'interface_usdt_net.py',
+    'interface_usdt_utxocache.py',
     'rpc_psbt.py --legacy-wallet',
     'rpc_psbt.py --descriptors',
     'rpc_users.py',