Increase coverage

We need to work a bit on coverage https://app.codecov.io/gh/fluiddyn/fluidsim

Remove from the fluidsim package

• fluidsim/solvers/ns2d/strat/find_dissipation.py
• fluidsim/base/dedalus
• fluidsim/base/basilisk

Run tests on Heptapod CI

• fluidsim/solvers/sphere

More/better testing

• fluidsim_core/output.py
• fluidsim_core/params.py
• fluidsim/base/preprocess/pseudo_spect.py
• fluidsim/util/console/bench_analysis.py
• fluidsim/operators/operators3d.py
• fluidsim/operators/op_finitediff2d.py
• fluidsim/base/output/phys_fields3d.py
• fluidsim/operators/operators2d.py
• fluidsim/solvers/sphere/sw1l/state.py