fix: do not call current_time for time-independent systems

[AayushSabharwal]

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

Add any other context about the problem here.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 26 lines in your changes are missing coverage. Please review.

Project coverage is 0.00%. Comparing base (8ebdf3f) to head (7f56f0d).

Files	Patch %	Lines
src/state_indexing.jl	0.00%	26 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #52       +/-   ##
==========================================
- Coverage   26.38%   0.00%   -26.39%     
==========================================
  Files           7       6        -1     
  Lines         235     236        +1     
==========================================
- Hits           62       0       -62     
- Misses        173     236       +63     

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