Make sync timeouts configurable

[tnull]

Previously, the timeouts applied to chain syncing weren't configurable
to users. While historically there were good reasons for this (mostly to
avoid leaving the Node in a blocked state for extended periods during
chain syncing), by now we should be good to let the users configure
timeouts ~freely, if they deem it fit. Here we allow for exactly that.

We also bump the previous defaults considerably, in the hopes that users now normally
shouldn't hit them ever.

[ldk-reviews-bot]

👋 Thanks for assigning @jkczyz as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

[jkczyz]

If there is an outstanding sync, do we skip a newly requested one?

[tnull]

Actually no, additional sync calls would subscribe and wait for the the pending sync to finish. The result will then be propagated via propagate_result_to_subscribers:

ldk-node/src/chain/mod.rs

Lines 56 to 83 in 5d83000

	fn propagate_result_to_subscribers(&mut self, res: Result<(), Error>) {
	// Send the notification to any other tasks that might be waiting on it by now.
	{
	match self {
	WalletSyncStatus::Completed => {
	// No sync in-progress, do nothing.
	return;
	},
	WalletSyncStatus::InProgress { subscribers } => {
	// A sync is in-progress, we notify subscribers.
	if subscribers.receiver_count() > 0 {
	match subscribers.send(res) {
	Ok(_) => (),
	Err(e) => {
	debug_assert!(
	false,
	"Failed to send wallet sync result to subscribers: {:?}",
	e
	);
	},
	}
	}
	*self = WalletSyncStatus::Completed;
	},
	}
	}
	}
	}

In case of a timeout that would be an Error::TxSyncTimeout.