zksend sdk fix network detection (#20268)

## Description 

Describe the changes or additions included in this PR.

## Test plan 

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---

## Release notes

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- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:
- [ ] REST API:

.changeset/curly-timers-wink.md

@@ -0,0 +1,5 @@
+---
+'@mysten/zksend': patch
+---
+
+fix zksend link network detection

sdk/zksend/src/links/claim.ts

@@ -124,17 +124,16 @@ export class ZkSendLink {
 	) {
 		const parsed = new URL(url);
 		const isContractLink = parsed.hash.startsWith('#$');
+		const parsedNetwork = parsed.searchParams.get('network') === 'testnet' ? 'testnet' : 'mainnet';
+		const network = options.network ?? parsedNetwork;
 
 		let link: ZkSendLink;
 		if (isContractLink) {
 			const keypair = Ed25519Keypair.fromSecretKey(fromBase64(parsed.hash.slice(2)));
 			link = new ZkSendLink({
 				...options,
 				keypair,
-				network:
-					options.network ?? parsed.searchParams.get('network') === 'testnet'
-						? 'testnet'
-						: 'mainnet',
+				network,
 				host: `${parsed.protocol}//${parsed.host}`,
 				path: parsed.pathname,
 				isContractLink: true,
@@ -143,14 +142,10 @@ export class ZkSendLink {
 			const keypair = Ed25519Keypair.fromSecretKey(
 				fromBase64(isContractLink ? parsed.hash.slice(2) : parsed.hash.slice(1)),
 			);
-
 			link = new ZkSendLink({
 				...options,
 				keypair,
-				network:
-					options.network ?? parsed.searchParams.get('network') === 'testnet'
-						? 'testnet'
-						: 'mainnet',
+				network,
 				host: `${parsed.protocol}//${parsed.host}`,
 				path: parsed.pathname,
 				isContractLink: false,