prepare condition functions

[LilithHafner]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Fixes SciML/diffeqpy#136.

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (0475fc3) 38.81% compared to head (4bfb5bf) 26.38%.

Files	Patch %	Lines
src/callbacks.jl	0.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #623       +/-   ##
===========================================
- Coverage   38.81%   26.38%   -12.44%     
===========================================
  Files          55       55               
  Lines        4261     4249       -12     
===========================================
- Hits         1654     1121      -533     
- Misses       2607     3128      +521     

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