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).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #6675   +/-   ##
=======================================
  Coverage     81.4%   81.5%           
=======================================
  Files          998     998           
  Lines        74456   74459    +3     
  Branches      7574    7558   -16     
=======================================
+ Hits         60624   60649   +25     
+ Misses       13832   13810   -22     

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 8 files with indirect coverage changes

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