Fix clippy lints

Author: cjdsellers

nautilus_core/portfolio/src/manager.rs

@@ -40,6 +40,7 @@ pub struct AccountsManager {
 }
 
 impl AccountsManager {
+    #[must_use]
     pub fn update_balances(
         &self,
         account: AccountAny,
@@ -49,6 +50,7 @@ impl AccountsManager {
         todo!()
     }
 
+    #[must_use]
     pub fn update_orders(
         &self,
         account: AccountAny,
@@ -59,6 +61,7 @@ impl AccountsManager {
         todo!()
     }
 
+    #[must_use]
     pub fn update_positions(
         &self,
         account: MarginAccount,