Refactor proxy settings and add error handling

[drew2a]

Reworked the 'set_proxy_settings' function in the download manager to handle invalid port values more gracefully. The function now attempts to convert the port value to an integer and logs any ValueError exceptions that occur during this process. This prevents crashes when non-integer values are provided for the port. Also, reorganized import statements according to PEP8 guidelines.

Additionally, a new test case 'test_set_proxy_settings_invalid_port' has been added to verify this behavior. It checks if proxy settings are not set when an invalid port number is provided.

Fixes #8014

[xoriole]

Under the possibility of server[1] being None which causes int(server[1]) to raise TypeError: int() argument must be a string, a bytes-like object or a real number, not 'NoneType', I would suggest to keep the initial if statement:

if server and server[0] and server[1]:

[drew2a]

You are right about the technical possibility of server[1] being None. This could be due to wrongly formatted settings. If we start considering these corner cases, then we should also check that the value of server has exactly two items, as it is technically possible to form an incorrect parameter. For example:

    fake_dlmgr.set_proxy_settings(session, 3, (None,))

To address these corner cases, I have to rewrite the function completely. Additional tests have also been added to highlight and test this possibility.