Refactor: replace valueFormatter with valueGetter for date formatting

[Creylay]

Summary

Fix date field display issue where date columns were not showing properly in DataGrid components. Replaced valueFormatter with valueGetter for consistent date formatting across dataset and model selection tables.

Type of change

• Bug fix.

Changes

• Fixed date field display in DatasetsTable component
• Fixed date field display in ExplorationsTable component
• Fixed date field display in ExplorationRunner component
• Fixed date field display in results page initialColumns
• Replaced valueFormatter: (params) => formatDate(params.value) with valueGetter: (value) => formatDate(value)

How to Test

1. Navigate to Datasets page and verify Created/Last Modified columns show dates properly
2. Check Explorations page tables for correct date formatting
3. Verify Results page shows all date columns (Created, Last Modified, Start, End) correctly
4. Confirm date fields are readable and properly formatted across all tables

Notes

This fix addresses the issue where date fields were not displaying correctly in DataGrid components due to using deprecated valueFormatter instead of the newer valueGetter API for MUI DataGrid date formatting.