tests: change Python code style to pass ruff checks

Most of the changes consisted of removing unused imports and unnecessary
f-strings.

tests: fix some Python typing issues

These otherwise raise errors in pytype. A few problematic methods
weren't being used and are deleted.

pytest: add ftp upload tests

- refs #13556
- allow anon uploads on vsftpd test server
- add test_30_05 for plain upload of 1k, 100k, 1m
- add test_31_05 for SSL upload of 1k, 100

pytest: add ftp upload tests

- refs #13556
- allow anon uploads on vsftpd test server
- add test_30_05 for plain upload of 1k, 100k, 1m
- add test_31_05 for SSL upload of 1k, 100k, 1m
- verify file size and contents

Closes #13734

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pytest: fixes for recent python, add FTP tests

Fixes:
- in uds tests, abort also silently on os errors
- be conservative on the h3 goaway duration
- detect curl debug build and u

pytest: fixes for recent python, add FTP tests

Fixes:
- in uds tests, abort also silently on os errors
- be conservative on the h3 goaway duration
- detect curl debug build and use in checks
- fix caddy version check for slight difference under linux
- set caddy default path fitting for linux
- fix deprecation warnings in valid time checks

FTP tests:
- add '--with-test-vsftpd=path' to configure
- use vsftpd default path suitable for linux
- add test_30 with plain FTP tests
- add test_31 with --ssl-reqd FTP tests
- add vsftpd to linux GHA for pytest workflows

Closes #13661

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