log_timed() has been updated to take in an optional logger argument

to specify a customer logger and extra to populate additional log

fields.
It also now works as a context manager, which handles stopping a log

when an exception occurs. This should simplify usage overall.
Every log_timed() call has a trace ID that can be used to associate

the beginning/end/result logs together. This is exposed on the timer

object so that other log calls can include it in their logs.
All arguments after message are now keyword-only. This will be

enforced in Djblets 7.
Deprecated calls for datetimes have been fixed. Typing has been added.

Documentation has been modernized to meet current standards. Unit tests

were added.

Unit tests pass.