Fix sponsor reserve accounting edge cases

[yinyiqian1]

High Level Overview of Change

• Disallows path-based sponsored account creation, so tfSponsorCreatedAccount cannot bypass the direct XRP payment reserve checks through SendMax / Paths.
• Corrects sponsored Vault reserve accounting so Vault sponsorship counts for 2 reserves: the Vault and its pseudo-account.
• Allow SponsorshipTransfer to modify Vault sponsor (NoPriv -> MayModifyVault)
• (Removed this commit because it duplicates 7542)Restricts NFTokenPage reserve sponsorship during NFTokenAcceptOffer so only buyer-submitted accepts can sponsor the buyer’s new NFTokenPage.

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 82.2%. Comparing base (d1a77b4) to head (09ce53d).

Additional details and impacted files

@@               Coverage Diff               @@
##           xrplf/sponsor   #7575     +/-   ##
===============================================
- Coverage           82.2%   82.2%   -0.0%     
===============================================
  Files               1016    1016             
  Lines              78401   78407      +6     
  Branches            9012    9014      +2     
===============================================
+ Hits               64440   64443      +3     
- Misses             13952   13955      +3     
  Partials               9       9             

Files with missing lines	Coverage Δ
include/xrpl/protocol/detail/transactions.macro	100.0% <ø> (ø)
...rotocol_autogen/transactions/SponsorshipTransfer.h	100.0% <ø> (ø)
src/libxrpl/tx/invariants/VaultInvariant.cpp	98.4% <100.0%> (+<0.1%)	⬆️
...rpl/tx/transactors/Sponsor/SponsorshipTransfer.cpp	90.2% <100.0%> (+0.1%)	⬆️
src/libxrpl/tx/transactors/payment/Payment.cpp	92.4% <100.0%> (+<0.1%)	⬆️

... and 2 files with indirect coverage changes

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