Add alpha parameter to DiceFocalLoss

[kephale]

Fixes #7682.

Description

This PR introduces the alpha parameter from FocalLoss into DiceFocalLoss.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• New tests added to cover the changes.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[ericspod]

Hi @kephale thanks for the contribution! I've made a few inline comments but in general it looks good. Please address these and I can come back to it for approval.

[kephale]

Okey doke, the requested changes have been addressed. I'm not sure what is going on with the min-dep tests because that part of the code hasn't been modified.

[ericspod]

The test fails are related to Numpy 2.0 being released a few days ago and we aren't compatible yet. I have a fix I need to push then these will work.

[ericspod]

I have pushed a temporary fix now so I'm rerunning your tests after merging dev into this branch.

[ericspod]

There is a DCO fail that you do need to fix, @kephale. The instructions are there if you click on the check.

[kephale]

The DCO should be addressed.

[KumoLiu]

/build

[KumoLiu]

Hi @ericspod, do you have any other comments on this one?

[ericspod]

I'm good here!