drop python<=3.7 support

[kloczek]

According to https://endoflife.date/python python 3.7 is EOSed since 27 Jun 2023.
Filter all code over pyupgrade --py38.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
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• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified