Use a real (probing-generated) scorer in benchmarks

[TheBlueMatt]

Until now, our routing benchmarks used a synthetic scorer, generated by scoring random paths to build up some history. This is pretty far removed from real-world routing conditions, as alternative paths generally have no scoring information and even the paths we do take have only one or two past scoring results.

Instead, we fetch a static serialized scorer, generated using minutely probes. This means future changes to the scorer's data may be harder to benchmark, but makes for substantially more realistic benchmarks for changes which don't impact the serialized state.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.04348% with 8 lines in your changes missing coverage. Please review.

Project coverage is 91.19%. Comparing base (2701bc5) to head (7ae311d).
Report is 66 commits behind head on main.

Files	Patch %	Lines
lightning/src/routing/router.rs	92.92%	5 Missing and 3 partials ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3103      +/-   ##
==========================================
+ Coverage   89.88%   91.19%   +1.31%     
==========================================
  Files         119      119              
  Lines       97551   106869    +9318     
  Branches    97551   106869    +9318     
==========================================
+ Hits        87681    97459    +9778     
+ Misses       7304     6921     -383     
+ Partials     2566     2489      -77     

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[tnull]

LGTM

Would be fine to land as-is from my side, still a few questions:

[TheBlueMatt]

Fixed the printed path:

$ git diff-tree -U1 cbe24bcb 3a462ef0
diff --git a/lightning/src/routing/router.rs b/lightning/src/routing/router.rs
index ca1281ec6..b904b7777 100644
--- a/lightning/src/routing/router.rs
+++ b/lightning/src/routing/router.rs
@@ -8494,3 +8494,3 @@ pub(crate) mod bench_utils {
 			"scorer-2023-12-10.bin",
-			"Please fetch https://bitcoin.ninja/ldk-scorer-v0.0.118-2023-12-10.bin and place it at scorer-2023-12-10.bin"
+			"Please fetch https://bitcoin.ninja/ldk-scorer-v0.0.118-2023-12-10.bin and place it at lightning/scorer-2023-12-10.bin"
 		);

[TheBlueMatt]

Dropped further redundant code:

$ git diff-tree -U10 3a462ef0 7ae311d6
diff --git a/lightning/src/routing/router.rs b/lightning/src/routing/router.rs
index b904b7777..f464c096e 100644
--- a/lightning/src/routing/router.rs
+++ b/lightning/src/routing/router.rs
@@ -8584,31 +8584,20 @@ pub(crate) mod bench_utils {
 				let path_exists =
 					get_route(&payer, &route_params, &graph.read_only(), Some(&[&first_hop]),
 						&TestLogger::new(), scorer, score_params, &random_seed_bytes).is_ok();
 				if path_exists {
 					route_endpoints.push((first_hop, params, amt_msat));
 					break;
 				}
 			}
 		}

-		// Because we've changed channel scores, it's possible we'll take different routes to the
-		// selected destinations, possibly causing us to fail because, eg, the newly-selected path
-		// requires a too-high CLTV delta.
-		route_endpoints.retain(|(first_hop, params, amt_msat)| {
-			let route_params = RouteParameters::from_payment_params_and_value(
-				params.clone(), *amt_msat);
-			get_route(&payer, &route_params, &graph.read_only(), Some(&[first_hop]),
-				&TestLogger::new(), scorer, score_params, &random_seed_bytes).is_ok()
-		});
-		route_endpoints.truncate(route_count);
-		assert_eq!(route_endpoints.len(), route_count);
 		route_endpoints
 	}
 }

 #[cfg(ldk_bench)]
 pub mod benches {
 	use super::*;
 	use crate::routing::scoring::{ScoreUpdate, ScoreLookUp};
 	use crate::ln::channelmanager;
 	use crate::ln::features::Bolt11InvoiceFeatures;