Telegram only auto-derives a voice/audio clip's duration from container
metadata for short recordings; clips longer than ~4:50 are delivered with
duration 0 and render as 0:00 in the player. Probe the length locally
(stdlib wave -> mutagen -> ffprobe) and pass duration explicitly to
sendVoice/sendAudio. Best-effort: when nothing can read the file we omit
duration and fall back to Telegram's prior behavior.
Extracts and hardens the Telegram-only part of the stale, Piper-bundled
PR #7815 (ffprobe-only, predates the send_voice retry/anchor refactor);
relates to #8508.
