Make Codec.get_dtype() an abstractmethod for consistency

All required codec methods (get_dtype, encode, decode) now use
@AbstractMethod to catch missing implementations at class definition
time rather than runtime.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: dimitri-yatsenko

src/datajoint/codecs.py

@@ -119,6 +119,7 @@ def __init_subclass__(cls, *, register: bool = True, **kwargs):
         _codec_registry[cls.name] = cls()
         logger.debug(f"Registered codec <{cls.name}> from {cls.__module__}.{cls.__name__}")
 
+    @abstractmethod
     def get_dtype(self, is_external: bool) -> str:
         """
         Return the storage dtype for this codec.
@@ -136,12 +137,10 @@ def get_dtype(self, is_external: bool) -> str:
 
         Raises
         ------
-        NotImplementedError
-            If not overridden by subclass.
         DataJointError
             If external storage not supported but requested.
         """
-        raise NotImplementedError(f"Codec <{self.name}> must implement get_dtype()")
+        ...
 
     @abstractmethod
     def encode(self, value: Any, *, key: dict | None = None, store_name: str | None = None) -> Any: