perf: Remove unnecessary caches

[bthomee]

High Level Overview of Change

NuDB and RocksDB internally already use caches, making the additional caches in the code not very valuable or even unnecessary. Moreover, some caches are defined but are not even used, which can also be removed.

Context of Change

The codebase contains many caches, and this PR is one of several to refactor the codebase with as goal to improve performance, such as reducing memory use, to support future account, trust line, and transaction growth.

This PR removes unnecessary caches in DatabaseNodeImp and SHAMapStoreImp; in the former we will instead rely on the caches built into the underlying NuDB or RocksDB stores, while the latter merely instantiated the caches but never used them. A performance analysis demonstrated that memory use reduced by 7%, CPU use increased by 2%, while all other metrics did not change significantly - a reasonable trade-off between memory and CPU. A more extensive performance analysis will be performed before this change is to be released.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

[codecov]

Codecov Report

Attention: Patch coverage is 23.07692% with 20 lines in your changes missing coverage. Please review.

Project coverage is 78.6%. Comparing base (70371a4) to head (d96c416).

Files with missing lines	Patch %	Lines
src/xrpld/nodestore/detail/DatabaseNodeImp.cpp	20.0%	20 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #5439   +/-   ##
=======================================
  Coverage     78.5%   78.6%           
=======================================
  Files          813     813           
  Lines        70084   69999   -85     
  Branches      8283    8262   -21     
=======================================
- Hits         55031   54985   -46     
+ Misses       15053   15014   -39     

Files with missing lines	Coverage Δ
src/xrpld/app/misc/SHAMapStoreImp.cpp	76.4% <100.0%> (-0.2%)	⬇️
src/xrpld/app/misc/SHAMapStoreImp.h	96.6% <ø> (ø)
src/xrpld/nodestore/detail/DatabaseNodeImp.h	73.9% <ø> (-5.0%)	⬇️
src/xrpld/nodestore/detail/DatabaseNodeImp.cpp	35.4% <20.0%> (+0.4%)	⬆️

... and 5 files with indirect coverage changes

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[PeterChen13579]

Just looping in @kuznetsss before approving, I don’t believe we do any node-level DB caching in Clio, right? So no changes should be needed on our side?

[kuznetsss]

As I understand this is rippled's internal database. So no changes on Clio's side are required.