fix: Address ai reviewer comments for delegation

[yinyiqian1]

Address AI review comments for #5825

High Level Overview of Change

Context of Change

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.5%. Comparing base (509677a) to head (5f64e0f).
⚠️ Report is 16 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #6675     +/-   ##
=========================================
- Coverage     81.5%   81.5%   -0.0%     
=========================================
  Files          998     998             
  Lines        74456   74459      +3     
  Branches      7578    7558     -20     
=========================================
+ Hits         60648   60649      +1     
- Misses       13808   13810      +2     

Files with missing lines	Coverage Δ
include/xrpl/protocol/TER.h	100.0% <ø> (ø)
src/libxrpl/protocol/Permissions.cpp	100.0% <100.0%> (ø)
.../libxrpl/tx/transactors/delegate/DelegateUtils.cpp	100.0% <100.0%> (ø)
src/libxrpl/tx/transactors/payment/Payment.cpp	93.5% <ø> (ø)

... and 4 files with indirect coverage changes

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[mvadari]

Hasn't this TODO blocker happened already?