feat: add %log start|off|on|state|level|stop for kernel logging

[maxandersen]

its notoriously hard to get kernel output so added ipython inspired %log commands magic
to enable better inspection.

with this the kernel can start adding logging more widespread for easier debugging.

Usage: %log <command>

Commands:
  start [filename] - Start logging to file (default: <kernelname>.log)
  stop             - Stop logging and close log file
  on               - Resume logging (if paused)
  off              - Pause logging (but keep file open)
  state            - Show current logging status
  level <LEVEL>    - Set logging level (SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST)

Examples:
  %log start                   - Start logging to <kernelname>.log
  %log start myapp.log         - Start logging to myapp.log
  %log off                     - Pause logging
  %log on                      - Resume logging
  %log state                   - Check status
  %log level WARNING           - Set logging level
  %log stop                    - Stop and close log file

[maxandersen]

any feedback/comments?