feat: add ParameterIndexingProxy

[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: 4 lines in your changes are missing coverage. Please review.

Comparison is base (f407c15) 24.85% compared to head (9189b4d) 24.30%.

Files	Patch %	Lines
src/parameter_indexing_proxy.jl	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #26      +/-   ##
==========================================
- Coverage   24.85%   24.30%   -0.55%     
==========================================
  Files           6        7       +1     
  Lines         177      181       +4     
==========================================
  Hits           44       44              
- Misses        133      137       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.