log_exception context manager avoids spamming by not logging every exception

[almarklein]

Every next exception that is the same as the first is shortened to a on-liner (we already had this).

After 5 messages we start to swallow messages, starting with an interval of 1 second, leading up to a max of 3 seconds between messages.

This helps avoid spamming the logger, which can also cause stalling on some systems. See #115 (comment)