type hints and linter improvements for v5

[totaam]

This is just a tracker ticket for improvements already made.

• mypy checks added using this config
  • now mostly complaining about ctypes, especially in the win32 modules - both are difficult to silence
• many new type hints
• fixes from sonarqube's linters

[totaam]

Somewhat related to #3592.

We can go further after v5 by dropping Python 3.6 support.

[totaam]

commits matching "type hint" using git log | grep -B 4 -ie "type.*hint" | grep -e "^commit " | awk '{print $2}' | xargs:
5529e73 102ead7 4b7a0ae 1b37c11 210db17 aef83e5 4ca2dc6 bcadc7f 983b9c3 ca12085 9ee5dba 2a908f5 bb7168d 7ba2917 cb40315 63191d3 e2fb986 e783ebf 2ba6866 9cef576 cb89b33 ccecd02 4300aa3 8bf9ce9 903bf7b ab46f1f 3517402 9188a41 961f290 f0807f7 ffbf35a 9a92de9 fe63a68 19fdbf9 a608b4c 45af6b1 5f39bcf 6b919a7 0fe546e ee32f2a 4f922e2 8a2dc78 5164ef6 1da6fe5 7c6dfc3 9a78a13 e2763bc 4170bfe aeeca14 fef8b55 4ab3123 cb65c7a 4d31502 0563e13 732eaaf cbb26db 0da3573 08acfb0 9231f28 9a3468d 5f9e35a 91bdd98 48d7e19 036168a cb235fc c4d5d60 81c3872 aec7901 9d68c24 6d6155b cdaafee dc5967f 5e72314 43c1925 742dc91 aa1f522 43bce37 d4a0488 4702cf5 bdb06eb 257ae3c c4b1403 f7b880e