Make QGTJacobian*** work when `Jax_disable_jit=1`

Created by: PhilipVinc

We don't officially support running netket with jax-jit disabled, but @alelovato recently tried doing it and It seems we just need this simple fix to make it work, so might as well add it.

Happens because without jit _choose_jacobian_mode returns a standard python int which does not have .item()