fix(generator): replace C# 10 inferred delegates with direct method calls for C# 9 compatibility

Generated code was using C# 10 "inferred delegate type" feature (var = method group)
which is incompatible with Unity's C# 9.0 support. This caused CS8773 errors when
building in Unity environments.

Changes:
- ArrayGenerator: Removed delegate variable declarations in monomorphic paths
- Replace indirect delegate calls with direct CachedSerializer/CachedDeserializer method calls
- Fixes serializer, deserializer (out), and deserializer (ref) code paths

Benefits:
- C# 9.0 compatible for Unity environments
- Zero delegate allocation overhead (performance improvement)
- Better JIT inlining potential with direct calls

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: JasonXuDeveloper

src/Nino.Generator/BuiltInType/ArrayGenerator.cs

@@ -95,14 +95,6 @@ protected override void GenerateSerializer(ITypeSymbol typeSymbol, Writer writer
             writer.AppendLine("    }");
             writer.AppendLine();
 
-            // Monomorphic fast path: cache the serializer delegate once
-            if (canUseMonomorphicPath)
-            {
-                writer.AppendLine("    // Monomorphic fast path: element type is sealed/struct, cache serializer");
-                writer.AppendLine($"    var serializer = CachedSerializer<{elementType.GetDisplayString()}>.SerializePolymorphic;");
-                writer.AppendLine();
-            }
-
             // Both value and reference types benefit from ref iteration - eliminates bounds checks
             writer.AppendLine("#if NET5_0_OR_GREATER");
             writer.AppendLine("    ref var cur = ref System.Runtime.InteropServices.MemoryMarshal.GetArrayDataReference(value);");
@@ -118,8 +110,8 @@ protected override void GenerateSerializer(ITypeSymbol typeSymbol, Writer writer
 
             if (canUseMonomorphicPath)
             {
-                // Use cached serializer directly
-                writer.AppendLine("        serializer(cur, ref writer);");
+                // Monomorphic fast path: direct call to avoid delegate allocation
+                writer.AppendLine($"        CachedSerializer<{elementType.GetDisplayString()}>.SerializePolymorphic(cur, ref writer);");
             }
             else
             {
@@ -258,27 +250,21 @@ protected override void GenerateDeserializer(ITypeSymbol typeSymbol, Writer writ
             writer.AppendLine(";");
             writer.AppendLine("    var span = value.AsSpan();");
 
-            // Monomorphic fast path: cache the deserializer delegate once
-            if (canUseMonomorphicPath)
-            {
-                writer.AppendLine("    // Monomorphic fast path: element type is sealed/struct, cache deserializer");
-                writer.AppendLine($"    var deserializer = CachedDeserializer<{elementType.GetDisplayString()}>.Deserialize;");
-            }
-
             writer.AppendLine("    for (int i = 0; i < length; i++)");
             writer.AppendLine("    {");
 
             if (canUseMonomorphicPath)
             {
+                // Monomorphic fast path: direct call to avoid delegate allocation
                 IfElseDirective(NinoTypeHelper.WeakVersionToleranceSymbol, writer,
                     w =>
                     {
                         w.AppendLine("        eleReader = reader.Slice();");
-                        w.AppendLine("        deserializer(out span[i], ref eleReader);");
+                        w.AppendLine($"        CachedDeserializer<{elementType.GetDisplayString()}>.Deserialize(out span[i], ref eleReader);");
                     },
                     w =>
                     {
-                        w.AppendLine("        deserializer(out span[i], ref reader);");
+                        w.AppendLine($"        CachedDeserializer<{elementType.GetDisplayString()}>.Deserialize(out span[i], ref reader);");
                     });
             }
             else
@@ -429,27 +415,21 @@ protected override void GenerateDeserializer(ITypeSymbol typeSymbol, Writer writ
             writer.AppendLine();
             writer.AppendLine("    var span = value.AsSpan();");
 
-            // Monomorphic fast path: cache the deserializer delegate once
-            if (canUseMonomorphicPath)
-            {
-                writer.AppendLine("    // Monomorphic fast path: element type is sealed/struct, cache deserializer");
-                writer.AppendLine($"    var deserializerRef = CachedDeserializer<{elementType.GetDisplayString()}>.DeserializeRef;");
-            }
-
             writer.AppendLine("    for (int i = 0; i < length; i++)");
             writer.AppendLine("    {");
 
             if (canUseMonomorphicPath)
             {
+                // Monomorphic fast path: direct call to avoid delegate allocation
                 IfElseDirective(NinoTypeHelper.WeakVersionToleranceSymbol, writer,
                     w =>
                     {
                         w.AppendLine("        eleReader = reader.Slice();");
-                        w.AppendLine("        deserializerRef(ref span[i], ref eleReader);");
+                        w.AppendLine($"        CachedDeserializer<{elementType.GetDisplayString()}>.DeserializeRef(ref span[i], ref eleReader);");
                     },
                     w =>
                     {
-                        w.AppendLine("        deserializerRef(ref span[i], ref reader);");
+                        w.AppendLine($"        CachedDeserializer<{elementType.GetDisplayString()}>.DeserializeRef(ref span[i], ref reader);");
                     });
             }
             else