api: remove data_format and simplify usages of get request

superfaktura/bank_account.py

@@ -31,6 +31,7 @@ Usage:
     bank.post(data)
 """
 
+import json
 from dataclasses import dataclass, asdict
 from typing import Optional
 
@@ -96,7 +97,8 @@ class BankAccount(SuperFakturaAPI):
     def list(self) -> dict:
         """Retrieves a list of bank accounts."""
         url = "bank_accounts/index"
-        return self.get(url)
+        bank_accounts = self.get(url)
+        return json.loads(bank_accounts)
 
     def default(self) -> Optional[BankAccountModel]:
         """Retrieves the default bank account."""