Add BMAT attack implementation (ECCV 2026)

[callous-youth]

Summary

• Add the BMAT implementation for transfer attacks.
• Register bmat in the attack zoo without modifying the existing main.py interface.
• Add BMAT to the README attack overview and untargeted benchmark table.

Implementation details

• The default configuration uses the released MBA pseudo-surrogate and MI-FGSM deployment updates.
• Input diversity remains optional and is disabled by default.
• higher==0.2.1 is loaded only when BMAT is instantiated, so existing attacks do not gain a new global dependency.
• Local checkpoints and Python bytecode are excluded via .gitignore.

Validation

• Verified BMAT module compilation and attack-zoo registration.
• Evaluated the default BMAT-MI configuration under the repository benchmark setting.