Make generated and reflective document members one rule

The generator and CultDocumentRegistry now discover members by the same
steps: most-derived declaration first, override chain collapsed to one
member, attributes read up the override chain, rejections in one order
with one text (GCC001 / InvalidOperationException).

- Accessors are named per document, so documents sharing a [CultName] or
  [CultIndex] base member no longer emit duplicate methods (CS0111).
- Duplicate [Key] slots are refused, including new-hidden fields and
  properties; a hidden persisted member with a different slot is refused.
- String [Key("x")] gets its own message instead of "has no [Key]".
- A persisted property whose set accessor is private, protected or init,
  or a readonly field, is refused instead of CS0272 in generated code.
- Overrides: MessagePack's DynamicObjectResolver reads the base
  declaration's [Key]/[IgnoreMember] (it throws "key is duplicated" for a
  re-keyed override and serializes an override marked [IgnoreMember]).
  An override that changes them is refused in both paths; an override
  that repeats or omits them is accepted and byte-pinned.
- Typed Serialize<T>/Deserialize<T> used static Options and skipped
  generated codecs and declared resolvers; deleted. CultNetDocumentBinding
  and CultMeshSnapshots route through the untyped path with their registry.

DocumentShapeSweepTests compiles each shape through the generator and
compares generated vs reflective schema id, catalog, name/index values
and payload against MessagePack's own bytes, or equal rejection text.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/GameCult.Caching.MessagePack/CultDocumentMessagePackSerialization.cs

@@ -69,16 +69,6 @@ public static class CultDocumentMessagePackSerialization
                    $"Formatter resolver {resolverType.FullName} needs a public static Instance or a public parameterless constructor and must implement {nameof(IFormatterResolver)}.");
     }
 
-    public static byte[] Serialize<T>(T value)
-    {
-        return MessagePackSerializer.Serialize(value, Options);
-    }
-
-    public static T Deserialize<T>(byte[] payload)
-    {
-        return MessagePackSerializer.Deserialize<T>(payload, Options);
-    }
-
     public static byte[] SerializeUntyped(object value, Type type)
     {
         return SerializeUntyped(value, type, CultDocumentRegistry.Shared);