Add the canonical MessagePack encoding for every public CultMath value type

CultMathResolver formats float2/3/4, double2/3, int2/3/4, bool2/3/4,
quaternion, Color32, Random, float2x2, float3x3, rect and CultCellular as
component arrays, and sits in the default CultCache resolver chain so no
consumer registers anything. It lives in GameCult.Caching.MessagePack, which
already owns that chain; CultMath core stays dependency-free.

Vector, rect and Aetheria-formatter byte shapes are pinned by golden tests, a
reflection test fails when a public CultMath value type has no formatter, and
decode skips extra elements and refuses nil.

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

src/GameCult.Caching.MessagePack/CultDocumentMessagePackSerialization.cs

@@ -57,7 +57,7 @@ public static class CultDocumentMessagePackSerialization
     {
         return MessagePackSerializerOptions.Standard
             .WithResolver(CompositeResolver.Create(
-                consumerResolvers.Append(CultDocumentResolver.Instance).Append(StandardResolver.Instance).ToArray()))
+                consumerResolvers.Append(CultDocumentResolver.Instance).Append(CultMathResolver.Instance).Append(StandardResolver.Instance).ToArray()))
             .WithSecurity(CultMessagePackSecurity.Instance);
     }