Update settings on change of backend

[rochisha0]

Updated functions to toggle between JAX and NumPy backends for solvers and dtype with corresponding method adjustments in QuTiP.

[coveralls]

Pull Request Test Coverage Report for Build 10484760873

Details

• 4 of 15 (26.67%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.7%) to 89.785%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/qutip_jax/settings.py	4	15	26.67%

Files with Coverage Reduction	New Missed Lines	%
src/qutip_jax/binops.py	1	96.5%

Totals
Change from base Build 9842191187:	-0.7%
Covered Lines:	1213
Relevant Lines:	1351

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💛 - Coveralls

[Ericgig]

Overall look good.

I am not a fan of the functions name... It set more than just the backend.
How about set_jax_as_default(*, revert=False) or set_as_default(*, revert=False)?

import qutip_jax
qutip_jax.use_as_default()
...
qutip_jax.use_as_default(revert=True)
...