Adds "fast with events" as default echem solver

[BradyPlanden]

Description

This PR updates the default solver for the echem models to include the "fast with events" mode. More information on this solver can be found:

https://github.com/pybamm-team/PyBaMM/blob/develop/pybamm/solvers/casadi_solver.py
https://docs.pybamm.org/en/stable/source/api/solvers/casadi_solver.html#casadi-solver

This is currently listed as experimental within the PyBaMM documentation, so I'm open to input on whether this should be blocked for a bit to ensure robustness.

Issue reference

Fixes #300

Review

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.80%. Comparing base (fed4a12) to head (02bd80a).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #301   +/-   ##
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  Coverage    95.79%   95.80%           
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  Files           38       38           
  Lines         2045     2048    +3     
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+ Hits          1959     1962    +3     
  Misses          86       86           

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[agriyakhetarpal]

Thanks, @BradyPlanden, would you also consider using numpy.testing.assert_allclose instead – it's the more recommended option nowadays, maybe not here, but in another PR, or here if you feel like it? The tolerances to check for would have to be adjusted in some test cases. I think the changes look good, though, and I'll let others review it too.

[martinjrobins]

changes look good, buth how have you found the "fast with events" solver compare against the idaklu solver? If events are important (e.g. in an experiment) the idaklu solver can be quite a bit faster.

[agriyakhetarpal]

The IDAKLU solver was tried in #176 and #217 and it's partially working for Unix-like platforms (with a non-repaired wheel and when built from source, so that's not ideal).

Windows support is probably still going to be broken for a while, because of the reasons described on the PyBaMM side where it doesn't work with pybamm.Interpolant and idaklu-cp3X-win-amd64.pyd cannot find the CasADi libs. I am not sure if it would work here or not – it might.

[martinjrobins]

fair enough! happy to stick with casadi then!