[python-qemu-qmp MR #12] Post-release trivial fix roundup

[GitLab Bot]

Author: John Snow - https://gitlab.com/jsnow
Merge Request: 
https://gitlab.com/qemu-project/python-qemu-qmp/-/merge_requests/12
... from: jsnow/python-qemu-qmp:fixes-roundup
... into: qemu-project/python-qemu-qmp:main

This MR collects a number of small, trivial fixes that follow the first 
official release; covering graceful exits if dependencies are missing, better 
interactive debugging information, and improving packaging, publishing and 
GitLab CI definitions.

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