Accepts Twilio's inbound WSS connections; parses the JSON envelope
(connected/start/media/stop per Twilio's documented protocol); decodes
base64 µ-law via G711Codec; ferries decoded PCM frames to a per-call
inbound mpsc. Concurrently drains the outbound mpsc + sends back JSON
media frames. Same tokio/std-thread split as slice-2's TapEngine: tokio
owns IO; the std thread owns the 20ms tick via trunk_driver::drive (T4).
ADR-0009 honored: TwilioCredentials never reach this module -- only
per-call CallSid (operational log correlation only) + tap_url (operator
configured brain WS URL) flow through the RegisterTrunkInboundChannel.
Signed-off-by: Aaron D. Lee <himself@adlee.work>