Moving mutex to partition level

[vlntb]

High Level Overview of Change

This change introduces two key optimizations:

1. Mutex scope reduction — Limits the lock to individual partitions within TaggedCache, reducing contention (see attached diagram illustrating the current bottleneck).
2. Decoupling — Removes tight coupling between LedgerHistory and TaggedCache, improving modularity and testability.

Lock Contention analysis based on eBPF shows significant improvements:

• 🔒 Held Mean Time: ↓ 60.17%
• ⏱ Held Max Time: ↓ 55.42%
• 🕒 Wait Mean Time: ↓ 38.74%
• ⚠️ Wait Max Time: ↑ 5.69%

Context of Change

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

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov]

Codecov Report

Attention: Patch coverage is 78.26087% with 15 lines in your changes missing coverage. Please review.

Project coverage is 78.4%. Comparing base (7ff4f79) to head (8e47907).

Files with missing lines	Patch %	Lines
include/xrpl/basics/TaggedCache.ipp	79.0%	13 Missing ⚠️
src/xrpld/app/ledger/LedgerHistory.cpp	33.3%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #5486     +/-   ##
=========================================
- Coverage     78.4%   78.4%   -0.1%     
=========================================
  Files          816     816             
  Lines        71715   71678     -37     
  Branches      8577    8600     +23     
=========================================
- Hits         56250   56183     -67     
- Misses       15465   15495     +30     

Files with missing lines	Coverage Δ
include/xrpl/basics/SHAMapHash.h	93.5% <ø> (ø)
include/xrpl/basics/TaggedCache.h	100.0% <ø> (ø)
include/xrpl/basics/partitioned_unordered_map.h	98.8% <100.0%> (-0.3%)	⬇️
src/xrpld/app/ledger/LedgerHistory.h	40.0% <ø> (ø)
src/xrpld/app/ledger/LedgerHistory.cpp	50.7% <33.3%> (-1.4%)	⬇️
include/xrpl/basics/TaggedCache.ipp	84.6% <79.0%> (-1.0%)	⬇️

... and 7 files with indirect coverage changes

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[vlntb]

This branch was tested with Antithesis, and no regressions were found.

[a1q123456]

Why do we want to return 0 here?