Unit tests and proposed fix for missing MultipleShooting attributes

[jcallaham]

Proposal to fix #186. Duplicate of #187 because I accidentally deleted the head branch and closed the first PR.

[codecov-commenter]

Codecov Report

Patch coverage: 83.33% and project coverage change: +2.07 :tada:

Comparison is base (6a0b830) 62.53% compared to head (c6664e3) 64.61%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #189 +/- ## ========================================== + Coverage 62.53% 64.61% +2.07% ========================================== Files 27 27 Lines 1879 1882 +3 ========================================== + Hits 1175 1216 +41 + Misses 704 666 -38 ``` | [Impacted Files](https://codecov.io/gh/DiffEqML/torchdyn/pull/189?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DiffEqML) | Coverage Δ | | |---|---|---| | [torchdyn/numerics/odeint.py](https://codecov.io/gh/DiffEqML/torchdyn/pull/189?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DiffEqML#diff-dG9yY2hkeW4vbnVtZXJpY3Mvb2RlaW50LnB5) | `45.91% <66.66%> (+3.11%)` | :arrow_up: | | [torchdyn/numerics/solvers/templates.py](https://codecov.io/gh/DiffEqML/torchdyn/pull/189?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DiffEqML#diff-dG9yY2hkeW4vbnVtZXJpY3Mvc29sdmVycy90ZW1wbGF0ZXMucHk=) | `84.78% <100.00%> (+10.36%)` | :arrow_up: | ... and [2 files with indirect coverage changes](https://codecov.io/gh/DiffEqML/torchdyn/pull/189/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DiffEqML) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DiffEqML). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DiffEqML)

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[Zymrael]

Thanks, looks great!