refactor(auth): refine duplicate OAuth credential checking logic

update the structure used for tracking processed OAuth emails during application lifespan initialization.

- The tracking dictionary now stores `email -> {provider: path}` instead of just `email -> path`.
- This ensures that duplicate credential warnings are only logged when multiple files for the *same* provider and email are found.
- Prevents false duplicate warnings when a user provides credentials for the same email across different OAuth services (e.g., Google and Microsoft).

src/proxy_app/main.py

@@ -164,7 +164,7 @@ async def lifespan(app: FastAPI):
 
     if not skip_oauth_init and oauth_credentials:
         logging.info("Validating OAuth credentials and checking for duplicates...")
-        processed_emails = {}
+        processed_emails = {} # email -> {provider: path}
         for provider, paths in oauth_credentials.items():
             provider_plugin_class = PROVIDER_PLUGINS.get(provider)
             if not provider_plugin_class: continue
@@ -189,10 +189,13 @@ async def lifespan(app: FastAPI):
                             
                             email = metadata.get("email")
                             if email:
-                                if email in processed_emails:
-                                    logging.warning(f"Duplicate credential for user '{email}' found at '{Path(path).name}'. Original at '{Path(processed_emails[email]).name}'.")
+                                if email not in processed_emails:
+                                    processed_emails[email] = {}
+                                if provider in processed_emails[email]:
+                                    original_path = processed_emails[email][provider]
+                                    logging.warning(f"Duplicate credential for user '{email}' on provider '{provider}' found at '{Path(path).name}'. Original at '{Path(original_path).name}'.")
                                 else:
-                                    processed_emails[email] = path
+                                    processed_emails[email][provider] = path
                 except Exception as e:
                     logging.error(f"Failed to process OAuth token for {provider} at '{path}': {e}")
         logging.info("OAuth credential processing complete.")

src/rotator_library/providers/gemini_auth_base.py

@@ -115,7 +115,6 @@ class GeminiAuthBase:
         lib_logger.debug(f"Initializing Gemini token for '{file_name}'...")
         try:
             creds = await self._load_credentials(creds_or_path) if path else creds_or_path
-            
             reason = ""
             if not creds.get("refresh_token"):
                 reason = "refresh token is missing"