Add burst guard to macOS route monitor

[dlon]

The route monitor currently immediately reacts to any route change. What happens is somewhat unpredictable because we're likely changing the routing table at the same time as the OS. We're also making many unnecessary changes to the routing table, and we might potentially end up constantly updating routes in a tight loop.

The PR fixes these issues by triggering route changes only after a minimum interval of time has elapsed.

Close DES-384.

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This change is 

[linear]

DES-384 Debounce route messages

It's difficult to get predictable results now, since we end up changing routes at the same time as the system adds or removes routes. Reusing the "burst guard" from the Windows routing code would likely help with this.

We should perhaps still synthesize a "default route removed" event whenever a network switch occurs to deal with DNS/macOS's connectivity check.

[pinkisemils]

Reviewed 6 of 6 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dlon)

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talpid-routing/src/debounce.rs line 93 at r1 (raw file):

    /// Asynchronously trigger burst
    pub fn trigger(&self) {
        self.sender.send(BurstGuardEvent::Trigger).unwrap();

This shouldn't unwrap, or stop and stop_nonblocking should take consume self instead of taking a reference.

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talpid-routing/src/unix/macos/mod.rs line 331 at r1 (raw file):

            | Ok(RouteSocketMessage::ChangeRoute(_))
            | Ok(RouteSocketMessage::AddAddress(_) | RouteSocketMessage::DeleteAddress(_)) => {
                self.update_trigger.trigger();

Ideally, the routes would be coalesced and we'd only react to changes in default routes - there's no need to take action if default routes have not been changed.

[pinkisemils]

Reviewed 1 of 1 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dlon)

[dlon]

Reviewable status: 4 of 6 files reviewed, 1 unresolved discussion (waiting on @pinkisemils)

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talpid-routing/src/debounce.rs line 93 at r1 (raw file):

Previously, pinkisemils (Emīls Piņķis) wrote…

This shouldn't unwrap, or stop and stop_nonblocking should take consume self instead of taking a reference.

Done.

[pinkisemils]

Reviewed 2 of 2 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved

[Jontified]

Reviewed 3 of 6 files at r1, 1 of 1 files at r2, 2 of 2 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved