Reintroduce `vectorcall` specialization for Python `call` API.

[Icxolu]

As part of the IntoPyObject migration process we removed the vectorcall optimization for simplicity for now in #4653. It was added in #4456 to speed up Python's call API by using the vectorcall calling convention where possible. This optimization was build on top of IntoPy which will be deprecated now in favor of IntoPyObject (#4618).

We'd like to reintroduce it in a future version using a separate PyCallArgs trait as discussed in #4456 (comment)