Add support for Python 3.12, drop EOL 3.7

[hugovk]

Changes proposed in this pull request:

• Python 3.12 is in beta
• Drop support for Python 3.7, EOL this month
  • https://devguide.python.org/versions/
  • https://peps.python.org/pep-0537/
• Not planning a major bump, requires-python = ">=3.8" makes sure people get the right version

[codecov]

Codecov Report

Merging #16 (7491074) into main (e1ed997) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main       #16   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines           60        60           
=========================================
  Hits            60        60           

Flag	Coverage Δ
macos-latest	100.00% <ø> (ø)
ubuntu-latest	100.00% <ø> (ø)
windows-latest	100.00% <ø> (ø)

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