chore(ci): Limit tokio/rayon pools for zk_toolbox CI (matter-labs#2828)

## What ❔

Limits rayon threadpool size to 2 and tokio threadpool size to 4 in
zk_toolbox CI.
I have checked locally, and with this configuration time to run
integration tests is pretty close to the default configuration.

## Why ❔

By default, both tokio and rayon will try to use all the CPUs. When we
run multiple Rust binaries at the same time (3 servers and 3 ENs in our
case), it causes a lot of conflict for resources, regardless of the
number of CPUs.

.github/workflows/ci-zk-toolbox-reusable.yml

@@ -4,14 +4,19 @@ on:
 
 env:
   CLICOLOR: 1
+  # We run multiple binaries in parallel, and by default they will try to utilize all the
+  # available CPUs. In tests, there is not much CPU-intensive work (rayon), but a lot of
+  # async work (tokio), so we prioritize tokio.
+  TOKIO_WORKER_THREADS: 4
+  RAYON_NUM_THREADS: 2
 
 jobs:
   lint:
     name: lint
     uses: ./.github/workflows/ci-core-lint-reusable.yml
 
   tests:
-    runs-on: [ matterlabs-ci-runner ]
+    runs-on: [ matterlabs-ci-runner-ultra-performance ]
     steps:
       - uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29 # v4
         with: