Compatibility to Python up to 3.14, two bugfixes, hardening

[halest]

Description

As discussed, this PR contains mostly maintenance, making the project compatible with Python up the the current latest version 3.14.

I ran the Testing Suite via Docker for all supported Python versions and each time, all tests turned green.

Updated dependencies.

When using the CLI, I added main guards to make usage easier

Also fixes two Bugs I stumbled across:

• Saving image and not manually typing an extension crashes in the background
• Creating a Color Barcode and then a Brightness Barcode crashes in the background when trying to load the second Barcode

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Maintenance

Checklist:

• My changes and comments follow the project's code of conduct
• I have made corresponding changes to the documentation
• There exists a test or I have included a test in the test suite to test changes.
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes