Migrate DICOM anonymization FPE from FF3 to FF1

[erinaldidb]

Summary

This PR migrates the DICOM anonymization format-preserving encryption implementation away from ff3/FF3-1 and onto fastfpe/FF1, updates the related documentation and demo notebook guidance, and expands anonymization test coverage around deterministic encryption, tweak handling, and metadata behavior.

Why this is required

NIST's February 2025 Draft 2 update to SP 800-38G Rev. 1 entirely withdraws FF3 and FF3-1 from the NIST standard due to published vulnerabilities. Because Pixels uses format-preserving encryption for DICOM de-identification, continuing to depend on FF3/FF3-1 would leave the accelerator aligned with a withdrawn construction. Migrating to FF1 keeps the anonymization workflow on the NIST-retained FPE mode.

Changes

• Replaces the ff3 dependency with fastfpe.
• Refactors DICOM anonymization code to use FF1-compatible encryption.
• Updates README and notebook documentation for the new fp_tweak behavior.
• Adds and updates tests for anonymization, imports, streaming helpers, and shared constants.
• Removes generated OHIF bundle content that triggered false-positive secret scan findings.

Validation

• Not run in this session.
• Full post-install integration validation is still required before merge per repo guidance, including dashboard, Genie, viewer/OHIF, MONAI proxy, gateway, model serving info/inference, and logs.

---

This PR was created with GitHub MCP.