Add `periodic_callable`

[basnijholt]

@jbweston, what about this? Closes #206.

I haven't really tested it but I suppose you can first see it this matches your use-case.

edit: I tested it and now it works

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 50.00000% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 74.40%. Comparing base (a8a8c48) to head (d8742e0). Report is 1 commits behind head on main.

Files	Patch %	Lines
adaptive_scheduler/_server_support/launcher.py	22.22%	7 Missing :warning:
adaptive_scheduler/_server_support/run_manager.py	83.33%	1 Missing :warning:
adaptive_scheduler/client_support.py	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #209      +/-   ##
==========================================
- Coverage   74.54%   74.40%   -0.15%     
==========================================
  Files          22       22              
  Lines        2742     2754      +12     
==========================================
+ Hits         2044     2049       +5     
- Misses        698      705       +7     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[jbweston]

Great! The only change I would add would be to pass the learner's "fname" along with the learner itself (like 'to_dataframe' takes)