nanobind 3.0 fails with Clang targeting Windows: dllimport vectorcall aliases are not constant expressions

nanobind 3.0.0 fails to compile with Clang targeting the Windows/MSVC ABI. The failure occurs in the new vectorcall aliases:

```cpp
inline constexpr ret (*name) args = ⌖
```
On Windows, PyObject_Vectorcall and PyObject_VectorcallMethod are imported functions. Clang does not consider their addresses constant expressions.

The MSVC-compiled CUDA extension succeeds; the same nanobind backend fails when compiled by ROCm Clang.

Pinning nanobind<3 resolves the build failure but is only a WAR that might get lost over time.

Start by reproducing the Windows-targeting ROCm Clang build with nanobind 3.0.0 and inspect the new vectorcall aliases for PyObject_Vectorcall and PyObject_VectorcallMethod. Done means the ROCm Clang extension compiles without pinning nanobind below 3, while the existing MSVC CUDA build still succeeds.

Written by the indexing model from the issue text.