Update data/model_handler.py

Fix dataset keyword naming from "training-size" to "train-size" in dataset_handler and model_handler

- Make sure train size and test size is not mulitply by 100

Add dataset nicknames for training and test sizes in get_datasets_nickname

Refactor model name handling in get_titan_data to use repo_id directly

Update TITAN leaderboard tab content and streamline data retrieval methods

Remove unused method _are_results_in_new_titan_format and streamline model name handling in get_titan_data

Refactor type hints in compute_initial_data and create_leaderboard_tab functions; update BLOCKLIST and USER in ModelHandler

Large refactor

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