Resolve TODO comments in socket utilities

[KaganCanSit]

Hello Botan Developer Team,

This pull request contains some TODO message resolves for socket utilities;

• Replaced inet_pton with string_to_ipv4 for IPv4 validation
  • Since there is a need for an additional parsing functions for IPv6 here, I have not updated ipv_6 for now.
• Implemented strerror_s per TODO comment - Windows
  • Uses 94-byte buffer as specified in Microsoft documentation
  • Thread-safe error string conversion

I don't except there to be any behavioral difference here. I believe I tested it by compiling with the following command on the Linux but need more additional testing. For Windows I will investigate the situation in CI.

ninja clean && ninja && python3 src/scripts/test_cli.py ./botan cli_tls

Regards.

[coveralls]

coverage: 90.669% (+0.002%) from 90.667%
when pulling e354b41 on KaganCanSit:remove-todos-socket-utilities
into 1fbc54f on randombit:master.

[reneme]

Some things regarding C-string handling, otherwise LGTM. Thank you!

[KaganCanSit]

Errors are appearing in Windows tests, but I don't think this is related to changes in this branch.

I occasionally see the message “Failure 1: Serpent producer 'avx512' unexpected result for encrypt” in the ‘Nightly’ build and other branches. I can retrigger CI with the “amend” comment without making any changes, or merge if appropriate.
Update: For this case, commit number 2cb6085 was included. I rebased branch.