doc: label header
refactor: replace isinstance(x, type(Y)) with (x, <type>)
chore: remove unused import errno
bug: roundup-server logs connection aborted for http 1.1 clients
chore(ruff): flow control; open context manager;
test: add testing for install_utils.py
refactor: use open context managers.
chore(ruff): whitespace, no Callable import, sorimports, add parens