Describe the bug

We should warn when noexcept is ignored - just to stop people thinking they're optimizing something that they aren't

Code to reproduce the behaviour:

cdef object xx() noexcept:
    pass

This also applies to memoryviews

Expected behaviour

This should generate a warning since exceptions are always checked for functions returning an object

OS

Linux

Python version

No response

Cython version

current master

Additional context

We might have to be a bit careful about fused functions - we probably don't want to generate warnings when some of the return types are valid for noexcept