DRAFT: Try yet another way to calculate loan payments

[ximinez]

High Level Overview of Change

• If payments remaining is X, compute the state for X-1
• Round those values
• Compute the payment components that will get us from the current state to the new state.
• Add or remove from the components to get as close to the fixed payment as possible.

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

❌ Patch coverage is 98.14815% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 78.8%. Comparing base (f4404ea) to head (6725b12).

Files with missing lines	Patch %	Lines
src/xrpld/app/misc/detail/LendingHelpers.cpp	98.1%	1 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##           ximinez/lending-XLS-66   #5941     +/-   ##
========================================================
- Coverage                    78.9%   78.8%   -0.0%     
========================================================
  Files                         838     838             
  Lines                       71302   71323     +21     
  Branches                     8439    8464     +25     
========================================================
- Hits                        56238   56225     -13     
- Misses                      15064   15098     +34     

Files with missing lines	Coverage Δ
include/xrpl/basics/Number.h	100.0% <ø> (ø)
src/libxrpl/basics/Number.cpp	99.5% <ø> (ø)
src/xrpld/app/misc/LendingHelpers.h	100.0% <ø> (ø)
src/xrpld/app/tx/detail/LoanSet.cpp	91.8% <100.0%> (ø)
src/xrpld/app/misc/detail/LendingHelpers.cpp	64.7% <98.1%> (-7.5%)	⬇️

... and 3 files with indirect coverage changes

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