Fix buffer protocol implementation

[QuLogic]

Description

According to the buffer protocol, ndim is a required field [1], and should always be set correctly. Additionally, shape should be set if flags includes PyBUF_ND or higher [2]. The current implementation only set those fields if flags was PyBUF_STRIDES.

~~Note, the tests currently leak, since they don't call PyBuffer_Release, as figuring out how to make a custom deleter work there is not something I've understood. Should I just immediately convert to a SimpleNamespace or similar instead or wrapping the struct?~~ I changed it to a SimpleNamespace.

[1] https://docs.python.org/3/c-api/buffer.html#request-independent-fields [2] https://docs.python.org/3/c-api/buffer.html#shape-strides-suboffsets

Suggested changelog entry:

* Fix buffer protocol implementation

PS, conventional commits are only mentioned in the PR template; they should be mentioned in https://github.com/pybind/pybind11/blob/af67e87393b0f867ccffc2702885eea12de063fc/.github/CONTRIBUTING.md so one knows that before committing...