memoryview Cross-Interpreter Data Has Some Minor Issues

# Bug report

### Bug description:

* dealloc is incomplete
* errors aren't handled quite right
* buffer not cleaned up if xidata never used
* some minor cleanup is needed


### CPython versions tested on:

CPython main branch

### Operating systems tested on:

_No response_


### Linked PRs
* gh-132779
* gh-132821
* gh-132960