default to single solver thread (#20266)

default to single solver thread (solving the proof is already multi-threaded)

Author: arvidn

chia/util/initial-config.yaml

@@ -655,7 +655,7 @@ solver:
   selected_network: *selected_network
 
   # Number of threads for solver operations
-  num_threads: 4
+  num_threads: 1
 
   # RPC server configuration
   rpc_port: 8667