Fix some typos after decorator removal

Co-authored-by: Andreas Klöckner <inform@tiker.net>

Drop dependency on, included obsolete copy of 'decorator' pypi module

Github: add py3.9 CI

Add keyed_memoize_in

Maintenance on memoize* decorators

ProcessLogger: account for sys.stdin being closed

- pytest overrides sys.stdin with DontReadFromInput

Better exception message when exceptions occur inside memoized methods

This avoid confusing error messages having
"During handling of the above exception, another exception occurred"

Avoid floating point zero in EOCRecorder