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[bot]]

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 :warning:

Additional details and impacted files

```diff @@ 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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