add C-API PyArray_IsAnyScalarExact

PyArray_IsAnyScalarExact checks if an object is exactly any numpy scalar, this allows skipping some costly attribute lookups like `__array_priority__` and `__numpy_ufunc__`.

this improves the array_scalar * numpy_scalar performance issue seen in gh-5030 by about a factor of two.
I guess a hash table wouldn't be any faster here.