docs: clarify dual-mode codecs in builtin_codecs docstring

- List <blob> and <blob@> separately to show both inline and external modes
- List <attach> and <attach@> separately to show both modes
- Change <hash> to <hash@> (external only)
- Change <object> to <object@> (external only)
- Clarify storage mode for each codec variant
- Also corrected hash algorithm from SHA256 to MD5

This makes it clear which codecs support dual modes vs external-only.

Author: dimitri-yatsenko

src/datajoint/builtin_codecs.py

@@ -6,12 +6,14 @@
 want to create their own custom codecs.
 
 Built-in Codecs:
-    - ``<blob>``: Serialize Python objects (internal) or external with dedup
-    - ``<hash>``: Hash-addressed storage with SHA256 deduplication
-    - ``<object>``: Schema-addressed storage for files/folders (Zarr, HDF5)
-    - ``<attach>``: File attachment (internal) or external with dedup
-    - ``<filepath@store>``: Reference to existing file in store
+    - ``<blob>``: Serialize Python objects (in-table storage)
+    - ``<blob@>``: Serialize Python objects (external with hash-addressed dedup)
+    - ``<attach>``: File attachment (in-table storage)
+    - ``<attach@>``: File attachment (external with hash-addressed dedup)
+    - ``<hash@>``: Hash-addressed storage with MD5 deduplication (external only)
+    - ``<object@>``: Schema-addressed storage for files/folders (external only)
     - ``<npy@>``: Store numpy arrays as portable .npy files (external only)
+    - ``<filepath@store>``: Reference to existing file in store (external only)
 
 Example - Creating a Custom Codec:
     Here's how to define your own codec, modeled after the built-in codecs::