feat: support zero-arg operators

[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	57fc261...	master / 57fc261...
ODEProblem	0.0886 ± 0.0061 s	0.0886 ± 0.0064 s	1 ± 0.1
init	0.0586 ± 0.0021 ms	0.0576 ± 0.0016 ms	1.02 ± 0.046
large_parameter_init/ODEProblem	0.969 ± 0.003 s	0.978 ± 0.01 s	0.99 ± 0.011
large_parameter_init/init	0.109 ± 0.0022 ms	0.109 ± 0.0023 ms	1 ± 0.029
mtkcompile	0.0327 ± 0.0024 s	31.5 ± 0.62 ms	1.04 ± 0.078
time_to_load	4.87 ± 0.033 s	4.91 ± 0.018 s	0.991 ± 0.0078

Memory benchmarks

	master	57fc261...	master / 57fc261...
ODEProblem	0.656 M allocs: 22 MB	0.655 M allocs: 22 MB	1
init	0.892 k allocs: 0.0461 MB	0.892 k allocs: 0.0461 MB	1
large_parameter_init/ODEProblem	4.16 M allocs: 0.163 GB	4.14 M allocs: 0.161 GB	1.01
large_parameter_init/init	1.74 k allocs: 0.0857 MB	1.74 k allocs: 0.0857 MB	1
mtkcompile	0.225 M allocs: 8.36 MB	0.225 M allocs: 8.35 MB	1
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	57fc261...	master / 57fc261...
ODEProblem	0.0995 ± 0.0089 s	0.1 ± 0.0056 s	0.994 ± 0.1
init	0.0444 ± 0.011 ms	0.0442 ± 0.011 ms	1.01 ± 0.35
large_parameter_init/ODEProblem	1.16 ± 0.033 s	1.19 ± 0.027 s	0.975 ± 0.035
large_parameter_init/init	0.0774 ± 0.016 ms	0.0784 ± 0.018 ms	0.987 ± 0.31
mtkcompile	0.0362 ± 0.0011 s	0.0364 ± 0.0013 s	0.995 ± 0.046
time_to_load	4.79 ± 0.072 s	4.78 ± 0.098 s	1 ± 0.026

Memory benchmarks

	master	57fc261...	master / 57fc261...
ODEProblem	0.67 M allocs: 22.1 MB	0.668 M allocs: 22 MB	1
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	4.38 M allocs: 0.162 GB	1
large_parameter_init/init	1.64 k allocs: 0.0596 MB	1.64 k allocs: 0.0596 MB	1
mtkcompile	0.231 M allocs: 7.91 MB	0.23 M allocs: 7.89 MB	1
time_to_load	0.149 k allocs: 11.1 kB	0.149 k allocs: 11.1 kB	1

[ChrisRackauckas]

The Hessian thing is unrelated but should be looked into.