[WIP] Make cache mutable struct

[Vaibhavdixit02]

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

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (35b97e5) 8.93% compared to head (2a893c3) 1.95%. Report is 36 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #674      +/-   ##
=========================================
- Coverage    8.93%   1.95%   -6.98%     
=========================================
  Files          31      31              
  Lines        2506    2501       -5     
=========================================
- Hits          224      49     -175     
- Misses       2282    2452     +170     

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