Update no_grad usage to inference_mode

[GuillaumeErhard]

I updated no_grad references in the repository to inference_mode for some slight performance gain.

References forno_grad / inference_mode difference:
https://discuss.pytorch.org/t/pytorch-torch-no-grad-vs-torch-inference-mode/134099/2?u=timgianitsos

https://stackoverflow.com/questions/74191070/why-are-there-two-different-flags-to-disable-gradient-computation-in-pytorch/74197846#74197846

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
segmentation_models_pytorch/base/model.py	83.56% <100.00%> (ø)
segmentation_models_pytorch/metrics/functional.py	28.85% <100.00%> (ø)

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[qubvel]

Looks good, thanks!