feat: new instance-based attack for data leakage in SVM/kNN models

[shamykyzer]

• New InstanceBasedAttack that extracts and compares support vectors (SVM) or stored neighbors (kNN) against training data to confirm data leakage
• Reports first 10 matches, mitigations, and detects DP-safe variants
• Supports sklearn Pipeline unwrapping

Closes [New Feature Request] New Attack: Model contains training data#59

[codecov]

Codecov Report

❌ Patch coverage is 94.14894% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.16%. Comparing base (42041fd) to head (da9ed7d).

Files with missing lines	Patch %	Lines
sacroml/attacks/instance_based_attack.py	94.11%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #431      +/-   ##
==========================================
- Coverage   99.51%   99.16%   -0.36%     
==========================================
  Files          23       24       +1     
  Lines        2687     2875     +188     
==========================================
+ Hits         2674     2851     +177     
- Misses         13       24      +11     

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