fix: MPT Transfer Fee shouldn't be bypassable via Small-Amount Escrow Rounding

[Kassaking7]

High Level Overview of Change

When an MPT-denominated EscrowFinish transaction computes the transfer fee owed to the issuer, it uses divideRound(amount, lockedRate, asset, roundUp=true) to compute the net amount delivered to the receiver. Rounding the net up implies rounding the fee down. For MPT (whose amounts are strict integers), and because the underlying canonicalizeRound approximation discards the fractional remainder after the intermediate divide-by-ten loops, the resulting fee collapses to exactly zero whenever the escrowed amount is small enough.

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

❌ Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
include/xrpl/ledger/helpers/EscrowHelpers.h	95.0%	1 Missing ⚠️

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