add a clarifying comment on try_calculate_account_len dedupe

Author: samkim-crypto

token/program-2022/src/extension/confidential_transfer/processor.rs

@@ -152,6 +152,8 @@ fn reallocate_for_configure_account_with_registry<'a>(
         let account = PodStateWithExtensions::<PodAccount>::unpack(&token_account)?;
         account.get_extension_types()?
     };
+    // `try_calculate_account_len` dedupes extension types, so always push
+    // the `ConfidentialTransferAccount` type
     current_extension_types.push(ExtensionType::ConfidentialTransferAccount);
     let needed_account_len =
         ExtensionType::try_calculate_account_len::<Account>(&current_extension_types)?;