memoryview Cross-Interpreter Data Has Some Minor Issues

[ericsnowcurrently]

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-132776: Minor Fixes for XIBufferViewType #132779
• gh-132776: Cleanup for XIBufferViewType #132821
• gh-132776: Revert Moving memoryview XIData Code to memoryobject.c #132960