fix(dsl): support class pointer arguments

[GrapeBaBa]

Summary

• make the class-pointer branch in convertArg comptime so *Class parameters reach unwrapChecked
• add JS DSL integration coverage for mutating a borrowed class pointer
• verify that passing a different wrapped class throws a TypeError before native access

Motivation

convertArg documents support for both class values and class pointers, but the pointer branch used a runtime if. Zig still analyzed the fallback @compileError, so exported functions accepting *Class could not compile. Consumers working around this with raw napi_unwrap can bypass zapi type-tag validation.