docs(codecs): fix stale storage-path and hash-algorithm docstrings

Three built-in codec class docstrings described pre-2.3.1 storage
layouts (and HashCodec claimed the wrong hash algorithm entirely):

- HashCodec: said 'SHA256'; actually MD5 + Base32
  (hash_registry.py:65-67). Layout said
  '_hash/{hash[:2]}/{hash[2:4]}/{hash}'; actually
  '{hash_prefix}/{schema}/{hash}' with hash_prefix defaulting to
  '_hash' and no [:2]/[:4] split anywhere in code.
- NpyCodec: layout said '{schema}/{table}/{pk}/{attribute}.npy';
  actually '{schema_prefix}/{schema}/{table}/{pk}/{attribute}_{token}.npy'
  after #1479 added the schema_prefix section and the random token
  suffix (via storage.build_object_path).
- ObjectCodec: same drift as NpyCodec, as a directory rather than a
  file.

All three docstrings had their 'Deletion:' line updated in v2.3.1
(dj.gc.collect() -> dj.gc.GarbageCollector) but the surrounding path
claims were left stale.

Docs-only.

Author: MilagrosMarin

src/datajoint/builtin_codecs/hash.py

@@ -1,5 +1,5 @@
 """
-Hash-addressed storage codec with SHA256 deduplication.
+Hash-addressed storage codec with MD5-based deduplication.
 """
 
 from __future__ import annotations
@@ -12,11 +12,13 @@
 
 class HashCodec(Codec):
     """
-    Hash-addressed storage with SHA256 deduplication.
+    Hash-addressed storage with content-addressed deduplication.
 
     The ``<hash@>`` codec stores raw bytes using hash-addressed storage.
-    Data is identified by its SHA256 hash and stored in a hierarchical directory:
-    ``_hash/{hash[:2]}/{hash[2:4]}/{hash}``
+    Data is identified by a 26-character Base32-encoded MD5 digest of the
+    content, and stored at ``{hash_prefix}/{schema}/{hash}`` (``hash_prefix``
+    defaults to ``_hash``). Stores with subfolding configured insert
+    additional path segments: ``{hash_prefix}/{schema}/{fold1}/{fold2}/{hash}``.
 
     The database column stores JSON metadata: ``{hash, store, size}``.
     Duplicate content is automatically deduplicated across all tables.

src/datajoint/builtin_codecs/npy.py

@@ -226,7 +226,9 @@ class NpyCodec(SchemaCodec):
     Schema-addressed storage for numpy arrays as .npy files.
 
     The ``<npy@>`` codec stores numpy arrays as standard ``.npy`` files
-    using schema-addressed paths: ``{schema}/{table}/{pk}/{attribute}.npy``.
+    using schema-addressed paths: ``{schema_prefix}/{schema}/{table}/{pk}/{attribute}_{token}.npy``
+    (``schema_prefix`` defaults to ``_schema``; ``{token}`` is a random
+    per-write suffix).
     Arrays are fetched lazily via ``NpyRef``, which provides metadata access
     without I/O and transparent numpy integration via ``__array__``.
 
@@ -269,7 +271,7 @@ class Recording(dj.Manual):
 
     Storage Details:
         - File format: NumPy .npy (version 1.0 or 2.0)
-        - Path: ``{schema}/{table}/{pk}/{attribute}.npy``
+        - Path: ``{schema_prefix}/{schema}/{table}/{pk}/{attribute}_{token}.npy``
         - Database column: JSON with ``{path, store, dtype, shape}``
 
     Deletion: Requires garbage collection via ``dj.gc.GarbageCollector``.

src/datajoint/builtin_codecs/object.py

@@ -15,7 +15,9 @@ class ObjectCodec(SchemaCodec):
     Schema-addressed storage for files and folders.
 
     The ``<object@>`` codec provides managed file/folder storage using
-    schema-addressed paths: ``{schema}/{table}/{pk}/{field}/``. This creates
+    schema-addressed paths: ``{schema_prefix}/{schema}/{table}/{pk}/{field}_{token}/``
+    (``schema_prefix`` defaults to ``_schema``; ``{token}`` is a random
+    per-write suffix). This creates
     a browsable organization in object storage that mirrors the database schema.
 
     Unlike hash-addressed storage (``<hash@>``), each row has its own unique path
@@ -51,7 +53,7 @@ def make(self, key):
     Storage Structure:
         Objects are stored at::
 
-            {store_root}/{schema}/{table}/{pk}/{field}/
+            {store_root}/{schema_prefix}/{schema}/{table}/{pk}/{field}_{token}/
 
     Deletion: Requires garbage collection via ``dj.gc.GarbageCollector``.