fix: don't override a transaction's recentBlockhash when calling simu…

…late if it's already set (#24280)

* Update simulate to add blockhash if not exist

Simulate has been overriding the recentBlockhash of the passed
Transaction which can be considered destructive and with side effects.

Since the purpose of this function is to purely simulate, it should not
override recentBlockhash if it has already been set

Refs solana-labs/solana#24279

* Apply prettier

src/connection.ts

@@ -3888,7 +3888,11 @@ export class Connection {
     } else {
       let disableCache = this._disableBlockhashCaching;
       for (;;) {
-        transaction.recentBlockhash = await this._recentBlockhash(disableCache);
+        if (!transaction.recentBlockhash) {
+          transaction.recentBlockhash = await this._recentBlockhash(
+            disableCache,
+          );
+        }
 
         if (!signers) break;