Reads link speed and RSSI from every SRC and RX over SSH. Safe to
run while audio is playing. On demand only — one SSH connection per
device, so this is not on a refresh timer.
Expect the numbers to move between runs. That is not the tool being
imprecise: a healthy link reports the same speed every time, so
variation is itself a finding.
Not implemented yet. Will measure throughput, loss under load and airtime share — and needs to stop audio first, so it will sit behind a confirmation.