Fix circular imports between helpers and validation

[grgmiller]

Purpose

Upstream repos using OGE were failing pytest due to circular imports in OGE between the helpers and validation module. This PR restructures the repo to avoid these circular imports, mostly by removing any calls to validation from the helpers module

What the code is doing

• Moves identify_percent_of_data_by_input_source from validation to output_data
• Moves some validation functions from helpers to the main data_pipeline
• Moves test_for_missing_subplant_id from validation to helpers since it is only used by a single function in helpers.

Testing

No testing yet. Not sure if there is an easy way to check whether any additional circular imports exist.

Review estimate

10 minutes

Future work

Implement test for circular imports?

Checklist

• Update the documentation to reflect changes made in this PR
• Format all updated python files using ruff
• Clear outputs from all notebooks modified
• Add docstrings and type hints to any new functions created