Neuralsde

[JuanKo96]

Opening the first PR for NeuralSDE for integrating sdeint into torchdyn. Also, as I formatted code files I have made changes using black, we can use this format for future uses if everyone likes it.

The goal is to substitute sdeint module from torchsde into torchdyn native version. Will open different PRs for Brownian Interval and adjoint methods(+ other methods if possible).

• [x] sdeint with fixed step size
• [x] NeuralSDE module able to run training
• [x] SDEFunc module for NeuralSDE
• [x] jupyter notebook for NeuralSDE cookbook

[codecov-commenter]

Codecov Report

Attention: 74 lines in your changes are missing coverage. Please review.

Comparison is base (c708c4c) 64.59% compared to head (0bbdd3e) 66.15%.

Files	Patch %	Lines
torchdyn/core/neuralde.py	54.90%	23 Missing :warning:
torchdyn/core/problems.py	61.22%	19 Missing :warning:
torchdyn/numerics/sdeint.py	78.12%	14 Missing :warning:
torchdyn/core/defunc.py	70.45%	13 Missing :warning:
torchdyn/numerics/solvers/sde.py	93.97%	5 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #166 +/- ## ========================================== + Coverage 64.59% 66.15% +1.55% ========================================== Files 27 29 +2 Lines 1881 2074 +193 ========================================== + Hits 1215 1372 +157 - Misses 666 702 +36 ```

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[JuanKo96]

This PR is ready to be merged.