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	1609d12...	master / 1609d12...
ODEProblem	0.0877 ± 0.0061 s	0.0895 ± 0.0063 s	0.98 ± 0.097
init	0.0579 ± 0.0015 ms	0.0579 ± 0.0015 ms	1 ± 0.037
large_parameter_init/ODEProblem	0.964 ± 0.0039 s	0.976 ± 0.0058 s	0.988 ± 0.0071
large_parameter_init/init	0.108 ± 0.0019 ms	0.109 ± 0.0022 ms	0.998 ± 0.027
mtkcompile	31.4 ± 1 ms	0.0323 ± 0.0017 s	0.972 ± 0.06
time_to_load	4.96 ± 0.027 s	4.95 ± 0.021 s	1 ± 0.0069

Memory benchmarks

	master	1609d12...	master / 1609d12...
ODEProblem	0.655 M allocs: 22 MB	0.659 M allocs: 22.1 MB	0.995
init	0.892 k allocs: 0.0461 MB	0.892 k allocs: 0.0461 MB	1
large_parameter_init/ODEProblem	4.17 M allocs: 0.163 GB	4.21 M allocs: 0.163 GB	0.997
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	1609d12...	master / 1609d12...
ODEProblem	0.101 ± 0.006 s	0.101 ± 0.0055 s	0.998 ± 0.081
init	0.0444 ± 0.011 ms	0.0444 ± 0.011 ms	1 ± 0.36
large_parameter_init/ODEProblem	1.2 ± 0.045 s	1.22 ± 0.021 s	0.98 ± 0.04
large_parameter_init/init	0.0783 ± 0.019 ms	0.0775 ± 0.019 ms	1.01 ± 0.35
mtkcompile	0.0385 ± 0.0021 s	0.0377 ± 0.0025 s	1.02 ± 0.088
time_to_load	4.89 ± 0.05 s	4.91 ± 0.048 s	0.996 ± 0.014

Memory benchmarks

	master	1609d12...	master / 1609d12...
ODEProblem	0.668 M allocs: 22 MB	0.673 M allocs: 22.2 MB	0.992
init	0.797 k allocs: 30.6 kB	0.797 k allocs: 30.6 kB	1
large_parameter_init/ODEProblem	4.41 M allocs: 0.163 GB	4.46 M allocs: 0.164 GB	0.994
large_parameter_init/init	1.64 k allocs: 0.0596 MB	1.64 k allocs: 0.0596 MB	1
mtkcompile	0.231 M allocs: 7.89 MB	0.234 M allocs: 8 MB	0.986
time_to_load	0.149 k allocs: 11.1 kB	0.149 k allocs: 11.1 kB	1