optimize `solver.jacobian__Fpsi__psi`
optimize `solver.jacobian__Fpsi__psi`

Use numpy arrays instead of lists.

Before::

    ncalls  tottime  percall  cumtime  percall
       966    1.512    0.002    2.794    0.003

After::

    ncalls  tottime  percall  cumtime  percall
       966    1.127    0.001    1.433    0.001

Further optimization is possible by caching the csr_matrix,
and only changing the diagonals. This will require a bit of
refactoring, though.

scott-maddox/obpds