feat: add discrete_inputs

[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.

[github-actions]

Benchmark Results (Julia vlts)

Time benchmarks

	master	400b048...	master / 400b048...
ODEProblem	0.0806 ± 0.012 s	0.078 ± 0.0077 s	1.03 ± 0.19
init	0.0537 ± 0.0017 ms	0.0534 ± 0.0017 ms	1.01 ± 0.046
large_parameter_init/ODEProblem	0.875 ± 0.031 s	0.846 ± 0.015 s	1.03 ± 0.042
large_parameter_init/init	0.102 ± 0.0032 ms	0.102 ± 0.0025 ms	1 ± 0.039
mtkcompile	27.1 ± 5.8 ms	27.8 ± 0.98 ms	0.974 ± 0.21
time_to_load	5.6 ± 0.27 s	5.22 ± 1 s	1.07 ± 0.22

Memory benchmarks

	master	400b048...	master / 400b048...
ODEProblem	0.655 M allocs: 22 MB	0.659 M allocs: 22.1 MB	0.994
init	0.892 k allocs: 0.0461 MB	0.892 k allocs: 0.0461 MB	1
large_parameter_init/ODEProblem	4.14 M allocs: 0.161 GB	4.24 M allocs: 0.165 GB	0.977
large_parameter_init/init	1.74 k allocs: 0.0857 MB	1.74 k allocs: 0.0857 MB	1
mtkcompile	0.225 M allocs: 8.35 MB	0.229 M allocs: 8.46 MB	0.987
time_to_load	0.153 k allocs: 14.5 kB	0.153 k allocs: 14.5 kB	1

[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	master	400b048...	master / 400b048...
ODEProblem	0.127 ± 0.029 s	0.0959 ± 0.0077 s	1.33 ± 0.32
init	0.0484 ± 0.012 ms	0.0427 ± 0.012 ms	1.13 ± 0.43
large_parameter_init/ODEProblem	1.42 ± 0.08 s	1.15 ± 0.025 s	1.23 ± 0.074
large_parameter_init/init	0.093 ± 0.027 ms	0.0736 ± 0.017 ms	1.26 ± 0.47
mtkcompile	0.0447 ± 0.0074 s	0.0362 ± 0.0035 s	1.24 ± 0.24
time_to_load	6.49 ± 0.75 s	5.5 ± 0.85 s	1.18 ± 0.23

Memory benchmarks

	master	400b048...	master / 400b048...
ODEProblem	0.669 M allocs: 22 MB	0.673 M allocs: 22.2 MB	0.994
init	0.797 k allocs: 30.6 kB	0.797 k allocs: 30.6 kB	1
large_parameter_init/ODEProblem	4.39 M allocs: 0.162 GB	4.48 M allocs: 0.165 GB	0.978
large_parameter_init/init	1.64 k allocs: 0.0596 MB	1.64 k allocs: 0.0596 MB	1
mtkcompile	0.231 M allocs: 7.9 MB	0.234 M allocs: 8 MB	0.987
time_to_load	0.149 k allocs: 11.2 kB	0.149 k allocs: 11.2 kB	1