[Rust SDK] Handle unwrap in wallet context (MystenLabs#18882)

## Description 

Handle unwrap in wallet context

## Test plan 

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## Release notes

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crates/sui-sdk/src/wallet_context.rs

@@ -183,7 +183,7 @@ impl WalletContext {
         budget: u64,
         forbidden_gas_objects: BTreeSet<ObjectID>,
     ) -> Result<(u64, SuiObjectData), anyhow::Error> {
-        for o in self.gas_objects(address).await.unwrap() {
+        for o in self.gas_objects(address).await? {
             if o.0 >= budget && !forbidden_gas_objects.contains(&o.1.object_id) {
                 return Ok((o.0, o.1));
             }