fix(mesh): poll TX_DONE and stuck-TX timeout from main loop

[DatanoiseTV]

The 60s stuck-TX detector in canSendImmediately only fires when more
packets enter the TX queue, because that's the only path that calls it.
If the queue empties after the radio wedges, no IRQ ever fires, no
poll runs, and the device sits in busyTx forever. pollMissedIrqs is
already invoked unconditionally from the main loop — extend it to
poll TX_DONE when sendingPacket is set, and trip the same reboot
path independently of queue activity.

Split out from #10424 per @thebentern's request — single-concern PR.

Build verification

pio run -e t-deck-tft succeeds, no new warnings.

Attestations

• I have tested that my proposed changes behave as described — review/static-analysis only, not on-air.
• On-hardware testing requested from community: build-verified t-deck-tft only.

[Copilot]

Pull request overview

This PR addresses a reliability gap in the RadioLib-based radio driver where the existing “stuck TX” watchdog only ran when new packets entered the TX queue. If the radio wedges after the queue drains and no TX IRQ fires, the node could remain in busyTx indefinitely. The change extends the already-main-loop-driven pollMissedIrqs() fallback to also poll for TX_DONE and to trigger the same stuck-TX reboot path even when the TX queue is empty.

Changes:

• Add a TX_DONE polling fallback (checkTxDoneIrqFlag) alongside the existing RX_DONE missed-IRQ polling.
• Extend pollMissedIrqs() to (a) poll TX_DONE while sendingPacket is set and (b) enforce the existing 60s stuck-TX reboot guard independent of TX queue activity.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/mesh/RadioLibInterface.h	Declares checkTxDoneIrqFlag() for missed TX_DONE polling support.
src/mesh/RadioLibInterface.cpp	Implements TX_DONE polling in pollMissedIrqs() and adds a queue-independent stuck-TX timeout/reboot trigger.