v3.3.2 - Cluster-safe worker heartbeats

Fixed

• Worker heartbeats are now Redis Cluster-safe. The heartbeat previously ran a multi-key Lua script over the worker hash and the worker index, whose keys hash to different slots, so a multi-shard cluster rejected every heartbeat with CROSSSLOT. The script now takes only the worker hash (the read-modify-write that must be atomic) and the index is updated with plain single-key commands afterwards; a missed index update self-heals on the next heartbeat. This closes the known limitation documented in v3.3.0's cluster support.