Increase the default liquidity_offset_half_life to six hours

Even at relatively high payment volumes, decaying knowledge of each
individual channel every hour causes aggressive retrying of
channels as we quickly forget the state of a channel. Even with the
historical tracker, this isn't fully remedied, as we'll track the
history bounds with the decayed value.

Instead, we decay every six hours here, reducing how often we'll
retry a channel due to decay.

In addition to this, the decay likely needs to be substantially
more linear, as tracked in lightningdevkit#1752.

lightning/src/routing/scoring.rs

@@ -411,7 +411,7 @@ pub struct ProbabilisticScoringParameters {
 	/// the available liquidity is halved and the upper-bound moves half-way to the channel's total
 	/// capacity.
 	///
-	/// Default value: 1 hour
+	/// Default value: 6 hours
 	///
 	/// # Note
 	///
@@ -596,7 +596,7 @@ impl ProbabilisticScoringParameters {
 			base_penalty_msat: 0,
 			base_penalty_amount_multiplier_msat: 0,
 			liquidity_penalty_multiplier_msat: 0,
-			liquidity_offset_half_life: Duration::from_secs(3600),
+			liquidity_offset_half_life: Duration::from_secs(6 * 60 * 60),
 			liquidity_penalty_amount_multiplier_msat: 0,
 			manual_node_penalties: HashMap::new(),
 			anti_probing_penalty_msat: 0,
@@ -619,7 +619,7 @@ impl Default for ProbabilisticScoringParameters {
 			base_penalty_msat: 500,
 			base_penalty_amount_multiplier_msat: 8192,
 			liquidity_penalty_multiplier_msat: 40_000,
-			liquidity_offset_half_life: Duration::from_secs(3600),
+			liquidity_offset_half_life: Duration::from_secs(6 * 60 * 60),
 			liquidity_penalty_amount_multiplier_msat: 256,
 			manual_node_penalties: HashMap::new(),
 			anti_probing_penalty_msat: 250,