fix: add missing stacklevel=2 to warnings.warn() calls in losses/ #8929

Problem

28 calls to warnings.warn() in monai/losses/ are missing the stacklevel parameter. Without stacklevel=2, warnings point to the MONAI internal code instead of the user's calling code, making it difficult for users to identify which part of their script triggered the warning.

Proposed Fix

Add stacklevel=2 to all 28 warnings.warn() calls in:

• monai/losses/dice.py (7 instances)
• monai/losses/tversky.py (3 instances)
• monai/losses/mcc_loss.py (3 instances)
• monai/losses/focal_loss.py (3 instances)
• monai/losses/hausdorff_loss.py (3 instances)
• monai/losses/unified_focal_loss.py (3 instances)
• monai/losses/spatial_mask.py (3 instances)
• monai/losses/perceptual.py (2 instances)
• monai/losses/adversarial_loss.py (1 instance)

Affected Files

• monai/losses/dice.py
• monai/losses/tversky.py
• monai/losses/mcc_loss.py
• monai/losses/focal_loss.py
• monai/losses/hausdorff_loss.py
• monai/losses/unified_focal_loss.py
• monai/losses/spatial_mask.py
• monai/losses/perceptual.py
• monai/losses/adversarial_loss.py