feat: add necessary initial conditions API

[AayushSabharwal]

Required for an upcoming MTK PR

[github-actions]

Benchmark Results (Julia vlts)

Time benchmarks

	master	15904e3...	master / 15904e3...
ODEProblem	6.45 ± 0.57 ms	6.27 ± 0.48 ms	1.03 ± 0.12
init	0.0979 ± 0.025 ms	0.0951 ± 0.027 ms	1.03 ± 0.39
large_parameter_init/ODEProblem	28.7 ± 4 ms	25.8 ± 2.7 ms	1.11 ± 0.19
large_parameter_init/init	0.106 ± 0.022 ms	0.107 ± 0.039 ms	0.987 ± 0.41
mtkcompile	11.4 ± 0.75 ms	11.2 ± 0.66 ms	1.02 ± 0.09
sparse_analytical_jacobian/ODEProblem	0.0353 ± 0.006 s	28.4 ± 2 ms	1.24 ± 0.23
sparse_analytical_jacobian/f_iip	1.89 ± 0.84 μs	1.82 ± 0.56 μs	1.04 ± 0.56
sparse_analytical_jacobian/f_oop	0.352 ± 0.0099 ms	0.348 ± 0.0098 ms	1.01 ± 0.04
time_to_load	5.52 ± 0.1 s	5.6 ± 0.15 s	0.986 ± 0.032

Memory benchmarks

	master	15904e3...	master / 15904e3...
ODEProblem	0.0392 M allocs: 2.01 MB	0.0392 M allocs: 2.01 MB	1
init	0.416 k allocs: 0.0697 MB	0.416 k allocs: 0.0697 MB	1
large_parameter_init/ODEProblem	0.326 M allocs: 11.6 MB	0.326 M allocs: 11.6 MB	1
large_parameter_init/init	0.604 k allocs: 0.172 MB	0.604 k allocs: 0.172 MB	1
mtkcompile	0.0616 M allocs: 3.45 MB	0.0616 M allocs: 3.45 MB	1
sparse_analytical_jacobian/ODEProblem	0.188 M allocs: 7.95 MB	0.188 M allocs: 7.95 MB	1
sparse_analytical_jacobian/f_iip	0 allocs: 0 B	0 allocs: 0 B
sparse_analytical_jacobian/f_oop	0.634 k allocs: 19.6 kB	0.634 k allocs: 19.6 kB	1
time_to_load	0.153 k allocs: 14.6 kB	0.153 k allocs: 14.6 kB	1

[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	master	a4a7401...	master / a4a7401...
ODEProblem	5.86 ± 0.74 ms	5.05 ± 0.51 ms	1.16 ± 0.19
init	0.073 ± 0.0077 ms	0.072 ± 0.0083 ms	1.01 ± 0.16
large_parameter_init/ODEProblem	23.6 ± 5.6 ms	21.9 ± 5.5 ms	1.08 ± 0.37
large_parameter_init/init	0.0751 ± 0.042 ms	0.0713 ± 0.04 ms	1.05 ± 0.83
mtkcompile	9.27 ± 0.7 ms	8.35 ± 0.62 ms	1.11 ± 0.12
sparse_analytical_jacobian/ODEProblem	22.9 ± 3.5 ms	20.8 ± 3.1 ms	1.1 ± 0.23
sparse_analytical_jacobian/f_iip	0.08 ± 0 μs	0.08 ± 0 μs	1 ± 0
sparse_analytical_jacobian/f_oop	0.12 ± 0.015 ms	0.117 ± 0.014 ms	1.03 ± 0.18
time_to_load	5.22 ± 0.053 s	5.3 ± 0.045 s	0.985 ± 0.013

Memory benchmarks

	master	a4a7401...	master / a4a7401...
ODEProblem	0.0392 M allocs: 1.81 MB	0.0392 M allocs: 1.83 MB	0.992
init	0.415 k allocs: 0.0517 MB	0.415 k allocs: 0.0517 MB	1
large_parameter_init/ODEProblem	0.356 M allocs: 13.1 MB	0.356 M allocs: 13.1 MB	1.01
large_parameter_init/init	0.798 k allocs: 0.151 MB	0.798 k allocs: 0.151 MB	1
mtkcompile	0.0581 M allocs: 2.75 MB	0.0581 M allocs: 2.75 MB	1
sparse_analytical_jacobian/ODEProblem	0.182 M allocs: 6.99 MB	0.182 M allocs: 6.99 MB	1
sparse_analytical_jacobian/f_iip	0 allocs: 0 B	0 allocs: 0 B
sparse_analytical_jacobian/f_oop	0.848 k allocs: 27 kB	0.848 k allocs: 27 kB	1
time_to_load	0.146 k allocs: 11.4 kB	0.146 k allocs: 11.4 kB	1