docs(tfhe-worker): document event test matrix modes

Author: Eikix

coprocessor/fhevm-engine/tfhe-worker/README.md

@@ -42,6 +42,7 @@ docker exec -u postgres -it fhevm-coprocessor-db-1 psql coprocessor
 ```
 cargo test
 ```
+`operators_from_events` uses the full type matrix by default. To run a lighter local matrix (up to `uint64`) set `TFHE_WORKER_EVENT_TYPE_MATRIX=local` before `cargo test`.
 
 ## Running the first working fhevm coprocessor smoke test