Let the host shell override RUST_LOG for the static test harness

The static suites hardcoded RUST_LOG=info, so raising the log level for a
node under test meant editing the compose file. Take it from the
environment with info as the default, matching the passthrough the same
block already uses for the worker-pool overrides.

Rendering is unchanged when RUST_LOG is unset, which is how CI invokes it.

testing/static/docker-compose.yml

@@ -33,7 +33,7 @@ x-fips-common: &fips-common
   env_file:
     - ./generated-configs${FIPS_CI_NAME_SUFFIX:-}/npubs.env
   environment:
-    - RUST_LOG=info
+    - RUST_LOG=${RUST_LOG:-info}
     # Passthrough for A/B benchmarking — set on the host shell before
     # `docker compose up` to override the worker-pool defaults.
     - FIPS_ENCRYPT_WORKERS=${FIPS_ENCRYPT_WORKERS:-}