bug#81561: 31.0.91; speedbar-window-mode creates stale idle timers

Daniel Mendler via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <[email protected]> writes:

> "J.P." <[email protected]> writes:
>
>> P.S. If it's determined that this bug is not in fact directly related to
>> the introduction of `speedbar-window-mode', perhaps it's better to
>> revert a56e964941f "Speedbar: no more stale idle timers (bug#81561)" on
>> Emacs 31 and instead apply any future attempted fixes to master?
>
> The bug is at least exacerbated by speedbar-window-mode. Basically
> speedbar-window-mode always causes a stale timer. Without window mode I
> see only few stale timers.
>
> I think using a kill-buffer-hook as Vincenzo proposed in his last patch
> is the way to go.

Makes sense. And it complements what `dframe-frame-mode' does with
`kill-buffer-hook' to perform teardown for `speedbar-frame-mode'. It
also seems likely (to me) that confining `dframe-set-timer' to
`speedbar-buffer' proves similarly important because `speedbar-timer-fn'
can otherwise run in any buffer when the thing fires.