feat: type-tag-aware unwrap and removeWrap

[nazarhussain]

Summary

• Adds unwrapChecked / removeWrapChecked to Env — thin wrappers that verify an object's type tag via napi_check_object_type_tag before unwrapping, returning error.InvalidArg on mismatch
• Existing unwrap / removeWrap remain unchanged (plain N-API wrappers)
• Adds examples/type_tag/ with a Cat/Dog example demonstrating how type tags prevent silently reinterpreting memory when the wrong this is passed to a native method

Motivation

When multiple classes use napi_wrap, passing the wrong JS object to a method silently casts the native pointer to the wrong type. Type tags (napi_type_tag_object + napi_check_object_type_tag) are the N-API solution for this, but the check-then-unwrap pattern is boilerplate unwrapChecked makes it a single explicit call.

Test plan

• zig build compiles all examples
• vitest run examples/type_tag/mod.test.ts — 3 tests pass (Cat, Dog, cross-type mismatch throws)

[wemeetagain]

this is quite frameworky (as in -- not part of napi, something you're adding on top) and needs to be documented somewhere

[nazarhussain]

I removed the implicit feature and added an explicit API with an example.

[lodekeeper-z]

Clean implementation. Type-tagged unwrap is exactly what we need for production NAPI bindings — prevents silent memory reinterpretation when JS passes wrong this. Good example coverage with the Cat/Dog test.

[wemeetagain]

This is a really nice addition :)