Refactor SegformerFinetuner to Use on_validation_epoch_end Hook

[SRDdev]

Description

This PR refactors the SegformerFinetuner class to ensure compatibility with PyTorch Lightning v2.0.0 by replacing the deprecated validation_epoch_end method with the on_validation_epoch_end hook. This change addresses the issue of maintaining compatibility with the latest PyTorch Lightning API.

Motivation:

• PyTorch Lightning v2.0.0 has deprecated the validation_epoch_end method, necessitating this update.
• This update ensures that validation metrics are computed and logged correctly using the new on_validation_epoch_end hook.

Relevant Links:

• PyTorch Lightning v2.0.0 release notes

Dependencies:

• None

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How has this change been tested, please provide a testcase or example of how you tested the change?

• Unit Testing: Ensured that all existing unit tests for the SegformerFinetuner class pass with the new implementation.
• Integration Testing: Conducted end-to-end tests to verify that the validation metrics are correctly computed and logged at the end of each epoch.
• Validation Outputs: Confirmed that validation outputs are properly cleared after each epoch to prevent data leakage.

Any specific deployment considerations

• No specific deployment considerations are required for this change. The updates are backward-compatible and do not introduce breaking changes.

Docs

• Docs updated? What were the changes:
  • No documentation updates were necessary as the changes are internal to the class implementation and do not affect the public API.

[CLAassistant]

All committers have signed the CLA.