godot-cpp: `PtrToArg::convert()` creates unnecessary copies

### Godot version

4.6.stable

### godot-cpp version

master

### System information

linux

### Issue description

The code for `PtrToArg` is pretty old and can be updated to not make copies
```cpp
#define MAKE_PTRARG(m_type) \
template <> \
struct PtrToArg { \
_FORCE_INLINE_ static m_type convert(const void *p_ptr) { \
return *reinterpret_cast(p_ptr); \
} \
}; \
template <> \
struct PtrToArg { \
_FORCE_INLINE_ static m_type convert(const void *p_ptr) { \
return *reinterpret_cast(p_ptr); \
} \
}
```
Stumbled upon this while thinking about why we needed internal getter https://github.com/godotengine/godot/pull/99201 , while it does looks like internal getter has its uses the engine itself had a similar issue https://github.com/godotengine/godot/issues/80074 and merged pr that prevented copying, so I figure `godot-cpp` can also stop copying arguments it got by a pointer where it doesn't need to make copies.

Also the engine itself is using even newer `PtrToArgDirect` and `PtrToArgByReference` where it doesn't make copies for arguments that can be passed by reference.

Tbh, it's just an enhancement, as `godot-cpp` will work correctly even without this, but in marshalling less copies is always better

### Steps to reproduce

Bind method with `const T &` argument

### Minimal reproduction project

N/A