The build now mounts the named volume inbuxa-server-cargo at /cache and keeps
CARGO_HOME and CARGO_TARGET_DIR there, so a push reuses the compiled
dependency tree (RocksDB included) instead of rebuilding it from scratch.
Both runners allow that one volume; each host keeps its own copy.
With the cache in place the job moves to runs-on: light, so it can run on
host2 as well. Cargo's parallelism now follows the job's CPU cap rather than
the host's core count, and the target dir is dropped past 25 GB.
jcoffey-dev