Refactor code for rounding numeric values of metrics

[elray1]

Consider a refactor of code for formatting numeric values into a helper function (rounding), and add unit tests

Here are 5 places where we round the value of a score. Could we just do it once?

• predevals/src/predevals.js

  Line 581 in f268127

  text_value = text_value.toFixed(get_round_decimals(col_name));

• predevals/src/predevals.js

  Line 745 in f268127

  hovertemplate: `model: %{data.name}<br>${thisState.selected_disaggregate_by}: %{x}<br>${score_col_name_to_text(this.state.selected_metric)}: %{y:.${get_round_decimals(this.state.selected_metric)}f}<extra></extra>`,

• predevals/src/predevals.js

  Line 782 in f268127

  colorbar_tick_format = `.${get_round_decimals(this.state.selected_metric)}f`;

• predevals/src/predevals.js

  Line 820 in f268127

  colorbar_tick_format = `.${get_round_decimals(this.state.selected_metric)}f`;

• predevals/src/predevals.js

  Line 911 in f268127

  hovertemplate: `${thisState.selected_disaggregate_by}: %{x}<br>model: %{y}<br>${score_col_name_to_text(this.state.selected_metric)}: %{customdata:.${get_round_decimals(this.state.selected_metric)}f}<extra></extra>`,

this is probably very low priority