Add clap CLI argument parsing with three log-level controls:
-q/--quiet errors only
(default) info — connections and value changes
-v debug — every packet's cmd/src/flags logged on TX and RX
-vv trace — full 32-byte hex dump of every packet on the wire
RUST_LOG env var continues to work as a fine-grained override for any
of the above levels.
Also expand the TX log line to include src and flags fields to match
the RX line, making the two symmetric.