Conditional logging

[ollie-etl]

Currently, Axis Frames (and presumably the other busses, I don't use them much), has a log statement in like this

self.log.info("TX frame: %s", frame)

However, regardless of log level, the log message is created, which isn't free. I've found that that checking the currently logging level prior to generating the log can lead to 3x sim speed ups. I have many, large data transfers occurring on wide busses.

if self.log.isEnabledFor(logging.DEBUG):
    self.log.debug("TX frame: %s", frame)
elif self.log.isEnabledFor(logging.INFO):
    self.log.info("TX frame: %s", frame.info())

The other improvement is to move the verbose dump into debug level, and provide a summary for info level, which doesn't include the data and tuser fields. I find this makes the logs significantly easier to work with. For instance, the verbose log output of my run will crash my terminal, presumably with out of memory errors, as they easily exceed 100k lines.

I'm happy to PR this, if there is interest and entusiam around this optimisation / API change?