go-xrpl: ParseMPTAmountBinary: positive MPT amount silently decoded as negative (int64 wrap)

go-xrpl is a Go implementation of the XRP Ledger protocol. In versions through the June 18, 2026 revision identified by the advisory, ParseMPTAmountBinary in internal/ledger/state/ripple_state.go converts the eight-byte MPT magnitude using num.Int64() without checking that it fits in 63 bits. A positive magnitude of at least 2^63 silently wraps into a negative amount without an error. ParseEscrow passes 33-byte sfAmount fields to the parser and stores MPTRaw() in EscrowData.MPTAmount, causing incorrect downstream calculations and divergence from rippled's interpretation of the same escrow entry. Independently, readMPTAmount in internal/tx/ledgerfields/decode_stream.go accepts over-limit magnitudes and surfaces large decimal strings without enforcing the maximum signed 64-bit value. The public codec in codec/binarycodec/types/amount.go already rejects these values, leaving the internal decoders inconsistent with that safe path. A source fix is available in commit 9dbd3935ed6c54f0232f2291edf9c012a0900dd5.