Add BERNN batch integration method

[spell00]

Describe your changes

This PR adds BERNN (Batch Effect Removal Neural Network) as a new method for the OpenProblems batch integration benchmark.

BERNN is a neural network-based approach designed to reduce technical batch effects while preserving biological information.

Changes include:

• Add the BERNN method implementation and Viash configuration.
• Register BERNN in the benchmark workflow.
• Update CHANGELOG.md.

Reference: https://doi.org/10.1038/s41467-024-48177-5

Checklist before requesting a review

• I have performed a self-review of my code

• Check the correct box. Does this PR contain:

  • Breaking changes
  • New functionality
  • Major changes
  • Minor changes
  • Bug fixes

• Proposed changes are described in the CHANGELOG.md

• CI Tests succeed and look good!