feat: debounce wants manually

[Stebalien]

Unfortunately, this is one of those cases in go where abstractions hurt more than they help.

This:

• Makes it easy to send immediately if we wait too long and/or if we have enough to send.
• Is significantly more efficient than the debounce library as it doesn't spin off a bunch of "after" timers.

fixes #245

[dirkmc]

Nice, this is a lot simpler 👍

I would like to abstract it out into its own class (in the messagequeue package) so as to more easily write tests for it. I will make a PR so we can see how it looks.

[dirkmc]

Note that this is slightly different from #254 in that sendMessageMaxDelay is only checked when the timer expires, so it's effectively a multiple of sendMessageDebounce. I prefer the simplicity of this approach so I think we should stick with it, but maybe we should explicitly define the max delay as a multiple of sendMessageDebounce, eg
sendMessageMaxDebounces := 100
^ nevermind I see that it preserves the time at which the debounce started so it's not necessarily a multiple of the debounce time

[dirkmc]

LGTM 👍

[Stebalien]

(we can continue discussing abstracting this in #256).