Compatibility with Python 3.12

[cgueret]

There is an error when loading the plug in with a Python 3.12 install:

  File "calibre_plugins.annotations.action", line 11, in <module>
    import imp, inspect, os, re, sys, tempfile, threading, types
ModuleNotFoundError: No module named 'imp'

And indeed, according to https://docs.python.org/3.11/library/imp.html, the module imp has been deprecated and removed in 3.12