Auto-recover a hung preamp on persistent I2C write failures

[stamateviorel]

What does this change intend to accomplish?

When the preamp microcontroller hangs it stops ACKing and every I2C write fails with OSError 121 (EREMOTEIO). The existing fallback in _Preamps.write_byte_data only reopens the SMBus handle, which recovers a transient bus glitch but not a hung preamp — zone control stays dead until someone power-cycles the unit. This escalates the fallback: when the reopened-bus retry also fails, reset the preamps in place, re-assign I2C addresses, reopen the bus, re-flush all cached register values (so zone mute/source/volume state survives the reset), then retry the write. Rate-limited to once per 20 s so a benign one-off glitch never resets audio.

We hit this live on 2026-06-04 (all zone control dead, reads OK / writes failing with Errno 121, only a reboot helped). With this patch deployed the same wedge self-heals in under a second.

Checklist

• Have you tested your changes and ensured they work? (in production on a real AmpliPi since 2026-06-04)
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• If applicable, have you updated the CHANGELOG?
• Does your submission pass linting & tests? (python -m py_compile clean; happy to fix anything CI flags)