perf(generator): add aggressive inlining to SerializeImpl/DeserializeImpl methods

Add MethodImpl(AggressiveInlining) attribute to generated Impl methods:

**SerializeImpl:**
- Mark SerializeImpl with AggressiveInlining attribute
- Ensures JIT compiler inlines these methods at call sites
- Critical for sealed type optimization to eliminate delegate overhead

**DeserializeImpl/DeserializeImplRef:**
- Mark both DeserializeImpl and DeserializeImplRef with AggressiveInlining
- Enables direct inlining when called from generated code
- Reduces call stack depth for sealed/struct deserialization

These attributes work in conjunction with the sealed type inlining optimization
to ensure the JIT can inline the complete serialization/deserialization logic,
eliminating all delegate and method call overhead for maximum performance.

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

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

Author: JasonXuDeveloper

src/Nino.Generator/Common/DeserializerGenerator.Trivial.cs

@@ -86,6 +86,7 @@ private void GenerateImpl(SourceProductionContext spc, StringBuilder sb, NinoTyp
         string suffix = byRef ? "Ref" : "";
 
         sb.AppendLine($$"""
+                                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                                 public static void DeserializeImpl{{suffix}}({{decl}} {{ninoType.TypeSymbol.GetTypeFullName()}} value, ref Reader reader)
                                 {
                                 #if {{NinoTypeHelper.WeakVersionToleranceSymbol}}

src/Nino.Generator/Common/SerializerGenerator.Trivial.cs

@@ -30,6 +30,7 @@ private void GenerateTrivialCode(SourceProductionContext spc, HashSet<ITypeSymbo
                     continue;
                 sb.AppendLine();
                 sb.AppendLine($$"""
+                                        [MethodImpl(MethodImplOptions.AggressiveInlining)]
                                         public static void SerializeImpl({{ninoType.TypeSymbol.GetTypeFullName()}} value, ref Writer writer)
                                         {
                                 """);