Copy Retry from invoice module to outbound_payment module

Also configure it such that in std tests, it will use SinceEpoch instead of
Instant so time can be manually advanced.

Author: valentinewallace

lightning/src/ln/outbound_payment.rs

@@ -187,6 +187,36 @@ impl PendingOutboundPayment {
 	}
 }
 
+/// Strategies available to retry payment path failures.
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub enum Retry {
+	/// Max number of attempts to retry payment.
+	///
+	/// Note that this is the number of *path* failures, not full payment retries. For multi-path
+	/// payments, if this is less than the total number of paths, we will never even retry all of the
+	/// payment's paths.
+	Attempts(usize),
+	#[cfg(not(feature = "no-std"))]
+	/// Time elapsed before abandoning retries for a payment.
+	Timeout(core::time::Duration),
+}
+
+impl Retry {
+	pub(crate) fn is_retryable_now(&self, attempts: &PaymentAttempts) -> bool {
+		match (self, attempts) {
+			(Retry::Attempts(max_retry_count), PaymentAttempts { count, .. }) => {
+				max_retry_count > count
+			},
+			#[cfg(all(not(feature = "no-std"), not(test)))]
+			(Retry::Timeout(max_duration), PaymentAttempts { first_attempted_at, .. }) =>
+				*max_duration >= std::time::Instant::now().duration_since(*first_attempted_at),
+			#[cfg(all(not(feature = "no-std"), test))]
+			(Retry::Timeout(max_duration), PaymentAttempts { first_attempted_at, .. }) =>
+				*max_duration >= SinceEpoch::now().duration_since(*first_attempted_at),
+		}
+	}
+}
+
 pub(crate) type PaymentAttempts = PaymentAttemptsUsingTime<ConfiguredTime>;
 
 /// Storing minimal payment attempts information required for determining if a outbound payment can