fix: resolve Windows path separator issue in Huawei OBS operations (#23475)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/libs/rsa.py

 import hashlib
-import os
 from typing import Union
 
 from Crypto.Cipher import AES
     pem_private = private_key.export_key()
     pem_public = public_key.export_key()
 
-    filepath = os.path.join("privkeys", tenant_id, "private.pem")
+    filepath = f"privkeys/{tenant_id}/private.pem"
 
     storage.save(filepath, pem_private)
 
 
 
 def get_decrypt_decoding(tenant_id: str) -> tuple[RSA.RsaKey, object]:
-    filepath = os.path.join("privkeys", tenant_id, "private.pem")
+    filepath = f"privkeys/{tenant_id}/private.pem"
 
     cache_key = f"tenant_privkey:{hashlib.sha3_256(filepath.encode()).hexdigest()}"
     private_key = redis_client.get(cache_key)