Force backend dtype to float

[bqth29]

💬 Pull Request Description

Based on #41, a reflexion was carried out regarding the difference between the models' dtype and the computation dtype.

Because the oscillators in the SB backend are in [-1, 1], the backend computation dtype must be a float. Besides, some key PyTorch methods are not available for float16 so only float32 and float64 are considered.

Thus, the core Ising model and the SB optimizer can only run on float32 or float64 dtype, any other dtype will raise a ValueError.

However, QuadraticPolynomials can still be of any dtype. When such a polynomial is converted to an Ising model:

• if the QuadraticPolynomial's dtype is float32 or float64, this dtype is used for the equivalent Ising model
• for any other dtype, the float32 dtype will be used for the Ising model by default

Once the optimal spins are retrieved by the polynomial at the end of the optimization and converted to integer values according to the optimization domain, the tensors are converted to the polynomial's dtype.

When passing the dtype parameter to the sb.maximize/sb.minimize functions, the dtype will be used as the QuadraticPolynomial's dtype and by extension as the optimization dtype if the dtype id float (otherwise, it will be float32).

Finally, for Polynomials, if the dtype and/or device parameters are set to None, the default dtype and/or device of PyTorch will be used.

✔️ Check list

• [x] The code matches the styling rules
• [x] The new code is covered by relevant tests
• [x] Documentation was added

🚀 New features

None.

🐞 Bug fixes

None.

📣 Supplementary information

None.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 98.61111% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 99.93%. Comparing base (54cf452) to head (01b3802).

Files	Patch %	Lines
src/simulated_bifurcation/check_dtype.py	87.50%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #62 +/- ## =========================================== - Coverage 100.00% 99.93% -0.07% =========================================== Files 36 38 +2 Lines 1600 1634 +34 =========================================== + Hits 1600 1633 +33 - Misses 0 1 +1 ```

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