Prefactor: Simplify state transitions, drop lock around PaymentQueue

The previous transition pattern of `OutboundJITChannelState` was never
great: we'd take `&mut self`, only to also return `Self` and required
updating the state externally to the state transtion methods. In
addition, we previously wrapped `PaymentQueue` in an `Arc<Mutex<..>>` to
avoid cloning them during state transtions.

Here, we clean up all of this, having the state transtion methods
updating the state in-place and merely returning an `action` in the
method's `Result`s. We also use `core::mem::take` to move the
`payment_queue` to the new states without reallocation.

Author: tnull

lightning-liquidity/src/lsps2/payment_queue.rs

@@ -6,18 +6,11 @@ use lightning_types::payment::PaymentHash;
 /// Holds payments with the corresponding HTLCs until it is possible to pay the fee.
 /// When the fee is successfully paid with a forwarded payment, the queue should be consumed and the
 /// remaining payments forwarded.
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Default, PartialEq, Eq, Debug)]
 pub(crate) struct PaymentQueue {
 	payments: Vec<(PaymentHash, Vec<InterceptedHTLC>)>,
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-pub(crate) struct InterceptedHTLC {
-	pub(crate) intercept_id: InterceptId,
-	pub(crate) expected_outbound_amount_msat: u64,
-	pub(crate) payment_hash: PaymentHash,
-}
-
 impl PaymentQueue {
 	pub(crate) fn new() -> PaymentQueue {
 		PaymentQueue { payments: Vec::new() }
@@ -55,6 +48,13 @@ impl PaymentQueue {
 	}
 }
 
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub(crate) struct InterceptedHTLC {
+	pub(crate) intercept_id: InterceptId,
+	pub(crate) expected_outbound_amount_msat: u64,
+	pub(crate) payment_hash: PaymentHash,
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;