Incorrect gamma default values in unified_focal_loss.py docstrings

[aymuos15]

Description

The docstrings in monai/losses/unified_focal_loss.py have incorrect default values for the gamma parameter. The code defaults are correct (matching the original author's implementation referenced in #4413), but the docstrings incorrectly state 0.75 for all classes.

Comparison with Original Implementation

Loss Function	Original Default γ	MONAI Code	MONAI Docstring
AsymmetricFocalLoss	2.0	gamma: float = 2 ✓	"Defaults to 0.75" ✗
AsymmetricFocalTverskyLoss	0.75	gamma: float = 0.75 ✓	"Defaults to 0.75" ✓
AsymmetricUnifiedFocalLoss	0.5	gamma: float = 0.5 ✓	"Defaults to 0.75" ✗

Specific Issues

1. AsymmetricFocalLoss (line 103, 111):

   • Code: gamma: float = 2
   • Docstring says: Defaults to 0.75

2. AsymmetricUnifiedFocalLoss (line 162, 171):

   • Code: gamma: float = 0.5
   • Docstring says: Defaults to 0.75

3. AsymmetricUnifiedFocalLoss also documents an epsilon parameter (line 172) that doesn't exist in the __init__ signature.

References

• Original paper: Unified Focal loss: Generalising Dice and cross entropy-based losses by Michael Yeung et al.
• Original implementation (referenced in Unified Focal Loss #4413): https://github.com/mlyg/unified-focal-loss/blob/main/loss_functions.py

Suggested Fix

Update the docstrings to match the actual code defaults (which are correct per the original implementation).

I am happy to create a PR if this fix is acceptable.