Refactor usage of PrivacyConfig in wrappers.py

[aviralgarg05]

PrivacyConfig is defined in src/agentunit/privacy/wrappers.py but is not actually used by PrivateDatasetWrapper.

Task:

• Update PrivateDatasetWrapper.__init__ to accept an optional PrivacyConfig object.
• Use values from the config (like enable_pii_masking, epsilon, etc.) instead of or in addition to individual arguments.
• Ensure consistency between the config dataclass and the wrapper's capabilities.