Better Encapsulate Scoring and Cache Point Count

[TheBlueMatt]

When we go to score a channel using the historical liquidity data, the first thing we do is step through all the valid bucket combinations, multiply the min and max bucket, and then add them together to calculate the total number of points tracked. This isn't a free operation, and for scorers without much data it represents a large part of the total time spent scoring during routefinding.

Thus, here we cache this value, updating it every time the buckets are updated. In order to do so, we first have to clean up scorer.rs, which has been needed for some time anyway, improving encapsulation so that caching is more reasonable.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.23810% with 8 lines in your changes missing coverage. Please review.

Project coverage is 89.70%. Comparing base (ccce9d9) to head (4fd07ec). Report is 23 commits behind head on main.

Files	Patch %	Lines
lightning/src/routing/scoring.rs	94.32%	8 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3188      +/-   ##
==========================================
+ Coverage   89.68%   89.70%   +0.01%     
==========================================
  Files         124      125       +1     
  Lines      102386   102458      +72     
  Branches   102386   102458      +72     
==========================================
+ Hits        91827    91912      +85     
+ Misses       7857     7843      -14     
- Partials     2702     2703       +1     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[TheBlueMatt]

LMK if I should squash.

[arik-so]

Yup, feel free to squash.

[TheBlueMatt]

Squashed without further changes.

[TheBlueMatt]

Rewrote the last commit message but didn't change the diff at all.

[TheBlueMatt]

Rebased