convert N column to numeric to ensure correct sort behavior

[elray1]

Currently, the data type of the N column is string, which means its values sort incorrectly, see screenshot:

We should change this data type to integer. This can be done somewhere in this block:

predevals/src/predevals.js

Lines 460 to 483 in f268127

	.then((data) => {
	// convert score columns to floats
	// TODO: extract to helper function for clarity
	for (const col_name of data.columns) {
	if (!['model_id', 'n', this.state.selected_disaggregate_by].includes(col_name)) {
	// This is a score column, so convert values in all rows to float
	for (let i = 0; i < data.length; i++) {
	data[i][col_name] = parseFloat(data[i][col_name]);
	// If it's an interval coverage column, multiply by 100
	if (interval_coverage_regex.test(col_name)) {
	data[i][col_name] *= 100;
	}
	}
	}
	}
	// update state
	if (isFetchScoresTable) {
	this.state.scores_table = data;
	} else{
	this.state.scores_plot = data;
	}
	})

See also #26 -- it could make sense to tackle these two issues together.