Use swap method that works with react-native

packages/xrpl/src/Wallet/rfc1751.ts

@@ -177,10 +177,14 @@ function bufferToArray(buf: Buffer): number[] {
  * @returns A buffer containing the same data with reversed endianness
  */
 function swap128(buf: Buffer): Buffer {
-  const result = Buffer.alloc(16)
-  result.writeBigUInt64LE(buf.readBigUInt64BE(0), 8)
-  result.writeBigUInt64LE(buf.readBigUInt64BE(8), 0)
-  return result
+  // Interprets buffer as an array of (two, in this case) 64-bit numbers and swaps byte order in-place.
+  const reversedBytes = buf.swap64()
+
+  // Swap the two 64-bit numbers since our buffer is 128 bits.
+  return Buffer.concat(
+    [reversedBytes.slice(8, 16), reversedBytes.slice(0, 8)],
+    16,
+  )
 }
 
 export { rfc1751MnemonicToKey, keyToRFC1751Mnemonic }