`integrate._ivp.base.OdeSolver` incomplete/missing annotations

[Huggzorx]

The OdeSolver class seems to be missing a y: onp.ArrayND[np.float64] attribute. The first overload of __init__ also gives t0: onp.ToFloatND but I believe it should be onp.ToFloat as in the second overload.

API reference: https://docs.scipy.org/doc/scipy/reference/generated/scipy.integrate.OdeSolver.html#scipy.integrate.OdeSolver

[jorenham]

Ah yea you'e right; apparently stubtest didn't pick up on that. It's a bit of a tricky one, because it can be either float64 or complex128, so I'm going to add a generic type parameter to OdeSolver that defaults to float64, but could also be set to complex128, or inferred as such.