refactor: remove protocol=='file' special case in exists() and isdir()

fsspec's local filesystem already handles exists() and isdir()
correctly for both files and directories. The protocol-specific
branches were unnecessary — self.fs.exists() and self.fs.isdir()
work uniformly across all backends including local files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/storage.py

@@ -555,7 +555,7 @@ def get_buffer(self, remote_path: str | PurePosixPath) -> bytes:
 
     def exists(self, remote_path: str | PurePosixPath) -> bool:
         """
-        Check if a file exists in storage.
+        Check if a path (file or directory) exists in storage.
 
         Parameters
         ----------
@@ -565,15 +565,11 @@ def exists(self, remote_path: str | PurePosixPath) -> bool:
         Returns
         -------
         bool
-            True if file exists.
+            True if the path exists.
         """
         full_path = self._full_path(remote_path)
         logger.debug(f"exists: {self.protocol}:{full_path}")
-
-        if self.protocol == "file":
-            return Path(full_path).exists()
-        else:
-            return self.fs.exists(full_path)
+        return self.fs.exists(full_path)
 
     def isdir(self, remote_path: str | PurePosixPath) -> bool:
         """
@@ -590,10 +586,7 @@ def isdir(self, remote_path: str | PurePosixPath) -> bool:
             True if the path is a directory.
         """
         full_path = self._full_path(remote_path)
-        if self.protocol == "file":
-            return Path(full_path).is_dir()
-        else:
-            return self.fs.isdir(full_path)
+        return self.fs.isdir(full_path)
 
     def remove(self, remote_path: str | PurePosixPath) -> None:
         """