Fix nonce length generation (MystenLabs#18081)

## Description 

Fixes nonce generation sometimes being off by one byte.

## Test plan 

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---

## Release notes

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that describes the impact of your changes that a user might notice and
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.changeset/flat-ligers-brush.md

@@ -0,0 +1,6 @@
+---
+'@mysten/sui': patch
+'@mysten/zklogin': patch
+---
+
+Fix nonce generation inconsistency

sdk/typescript/src/zklogin/index.ts

@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 export { getZkLoginSignature, parseZkLoginSignature } from './signature.js';
-export { toBigEndianBytes } from './utils.js';
+export { toBigEndianBytes, toPaddedBigEndianBytes } from './utils.js';
 export { computeZkLoginAddressFromSeed } from './address.js';
 export { toZkLoginPublicIdentifier, ZkLoginPublicIdentifier } from './publickey.js';
 export type { ZkLoginSignatureInputs } from './bcs.js';

sdk/zklogin/src/nonce.ts

@@ -3,7 +3,7 @@
 
 import { toHEX } from '@mysten/bcs';
 import type { PublicKey } from '@mysten/sui/cryptography';
-import { toBigEndianBytes } from '@mysten/sui/zklogin';
+import { toPaddedBigEndianBytes } from '@mysten/sui/zklogin';
 import { randomBytes } from '@noble/hashes/utils';
 import { base64url } from 'jose';
 
@@ -29,7 +29,7 @@ export function generateNonce(publicKey: PublicKey, maxEpoch: number, randomness
 	const eph_public_key_0 = publicKeyBytes / 2n ** 128n;
 	const eph_public_key_1 = publicKeyBytes % 2n ** 128n;
 	const bigNum = poseidonHash([eph_public_key_0, eph_public_key_1, maxEpoch, BigInt(randomness)]);
-	const Z = toBigEndianBytes(bigNum, 20);
+	const Z = toPaddedBigEndianBytes(bigNum, 20);
 	const nonce = base64url.encode(Z);
 	if (nonce.length !== NONCE_LENGTH) {
 		throw new Error(`Length of nonce ${nonce} (${nonce.length}) is not equal to ${NONCE_LENGTH}`);