Add note on protocol arg coercion timing
Nb protocol: coerce bytestrings at request-enqueue time

I.e. rather than at `wcar` resolution (send) time. This is important to
support arb (non-string) Cluster keyslot hashing, sensible per-command
thread-local environment support, etc.
Cluster: support key hashing over arbitrary (non-string) keys
Update dependencies
Fix `atomic` exception handling
WIP cluster execute-requests
WIP rework execute-requests