Remove extra config validation

[guarin]

What has changed and why?

• Remove extra config validation

Removes an extra config validation step which converted all configs to TrainTaskConfig. The extra validation is no longer necessary as we already validate the config in _train_task (5 lines above the change). The extra validation also resulted in all config classes getting converted to TrainTaskConfig instances instead of keeping their original class, e.g. ObjectDetectionConfig. This didn't result in any bugs because we never rely on the instance type of the config but avoiding the conversion is clearly the better solution and prevents future bugs.

How has it been tested?

• Manually

Did you update CHANGELOG.md?

• Yes
• Not needed (internal change)

Did you update the documentation?

• Yes
• Not needed (internal change without effects for user)

[guarin]

/review

[Copilot]

Pull request overview

Removes a redundant second Pydantic validation/conversion step in the training command flow so the original config model type (e.g., ObjectDetectionConfig) is preserved, relying on the existing validation already performed in _train_task.

Changes:

• Removed re-validation/re-construction of config into TrainTaskConfig inside _train_task_from_config.
• Ensures the config instance type remains the specific config_cls produced by _train_task validation.