fix(protocols): revert #2432's RegistryError message to name Protocol (#2434)

#2432 (round 10 of #1103) changed register's RegistryError message from
"...must be a Protocol subclass" to "...must be a ProtocolBase subclass"
in pcapkit/protocols/protocol.py and foundation/registry/protocols.py, and
updated the locked assertions in tests/protocols/test_register_class_guard_unit.py
and tests/foundation/registry/test_protocols.py to match. This was a mistake.

* The wording naming Protocol (not ProtocolBase) is a deliberate, ratified
  decision: #1016 ruled the message's reader is third-party code, who should
  be told to subclass Protocol -- ProtocolBase's own docstring says it is
  "for internal use only". The owner approved that reasoning, #2316
  re-confirmed it as out of scope to change, and #2420's commit explicitly
  records "the error message names Protocol" as the kept half of the split
  between the Raises: clause (ProtocolBase) and the raised message
  (Protocol). #2420 also notes it already caught and corrected one prior
  accidental flip of this exact wording.
* Reverted both raise sites and the four locked test assertions back to
  "Protocol subclass".
* Also fixed a citation left by #2432: tests/foundation/reassembly/
  test_deferred_pickle_2423_unit.py cited :issue:`2424` (the merged PR, not
  an issue) where it meant the underlying fix, tracked as #2423 -- matches
  the file's existing :issue:`2423` citation style and the changelog's own
  "(:issue:`2423`, :issue:`2425`, :pr:`2424`)" citation.

#2432's other two fixes (a stale docstring, a cross-reference to a moved
EnumField) are correct and untouched.

Refs #1016, #2316, #2420
Refs #1103

Build: tests/protocols/test_register_class_guard_unit.py,
tests/foundation/registry/test_protocols.py,
tests/foundation/reassembly/test_deferred_pickle_2423_unit.py pass; full
tests/project/ run shows no new failures (13 pre-existing failures, all in
unrelated subprocess/network-dependent tests, none touching these files).

Author: JarryShaw

pcapkit/foundation/registry/protocols.py

@@ -221,7 +221,7 @@ class rather than supplied by a caller, and this function is the funnel
     if not isinstance(protocol, type):
         raise RegistryError(f'protocol must be a class, not {protocol!r}')
     if not issubclass(protocol, ProtocolBase):
-        raise RegistryError(f'protocol must be a ProtocolBase subclass, not {protocol!r}')
+        raise RegistryError(f'protocol must be a Protocol subclass, not {protocol!r}')
 
     name = protocol.__name__.upper()
     incumbent = protocol_registry.get(name)

pcapkit/protocols/protocol.py

@@ -1139,7 +1139,7 @@ def _next_layer_entry(cls, code: 'Any', protocol: 'ModuleDescriptor[ProtocolBase
         if not isinstance(protocol, type):
             raise RegistryError(f'protocol must be a class, not {protocol!r}')
         if not issubclass(protocol, ProtocolBase):
-            raise RegistryError(f'protocol must be a ProtocolBase subclass, not {protocol!r}')
+            raise RegistryError(f'protocol must be a Protocol subclass, not {protocol!r}')
         return protocol
 
     @classmethod

tests/foundation/reassembly/test_deferred_pickle_2423_unit.py

@@ -245,7 +245,7 @@ def test_setstate_still_accepts_the_first_revisions_flat_shape(self) -> None:
         """The flat ``{slot: value}`` shape the very first fix returned.
 
         Never released, but already pushed in an earlier revision of
-        :issue:`2424`'s fix -- accepting it costs nothing and protects anyone
+        :issue:`2423`'s fix -- accepting it costs nothing and protects anyone
         who pickled against that revision.
 
         """

tests/foundation/registry/test_protocols.py

@@ -438,7 +438,7 @@ def test_register_protocol_rejects_a_non_class_with_registry_error(self) -> None
             ('none', None, 'must be a class'),
             ('descriptor argument (not unwrapped here)',
              ModuleDescriptor('pcapkit.protocols.misc.raw', 'Raw'), 'must be a class'),
-            ('wrong class', object, 'ProtocolBase subclass'),
+            ('wrong class', object, 'Protocol subclass'),
         ):
             with self.subTest(value=label):
                 with self.assertRaises(RegistryError) as caught:

tests/protocols/test_register_class_guard_unit.py

@@ -82,7 +82,7 @@ def test_wrong_class_still_raises_registry_error(self) -> None:
                 with mock.patch.dict(klass.__proto__):
                     with self.assertRaises(RegistryError) as caught:
                         klass.register(code, dict)  # type: ignore[arg-type]
-                self.assertIn('ProtocolBase subclass', str(caught.exception))
+                self.assertIn('Protocol subclass', str(caught.exception))
 
     def test_descriptor_naming_a_non_class_raises_registry_error(self) -> None:
         from pcapkit.corekit.module import ModuleDescriptor
@@ -107,7 +107,7 @@ def test_descriptor_naming_a_wrong_class_still_raises_registry_error(self) -> No
                 with mock.patch.dict(klass.__proto__):
                     with self.assertRaises(RegistryError) as caught:
                         klass.register(code, descriptor)  # type: ignore[arg-type]
-                self.assertIn('ProtocolBase subclass', str(caught.exception))
+                self.assertIn('Protocol subclass', str(caught.exception))
 
     def test_valid_class_and_descriptor_still_register(self) -> None:
         from pcapkit.corekit.module import ModuleDescriptor