copies across visual changes from inputs app to the rates funnel plot

[tomjemmett]

• extend x-limits of the control lines to epand off edge of plot area (like centre line)
• adds more variables to control the colour/style of the control lines

[Copilot]

Pull request overview

Updates the rates funnel plot styling/ranges to match visual behavior from the inputs app, specifically extending control-limit lines and making their styling more configurable in-code.

Changes:

• Adds separate line-type/colour variables for centre line, 2-sigma, and 3-sigma control lines.
• Extends the x-range for control-limit geom_function() layers so they draw beyond the visible panel edge.
• Sets an explicit x-range on the plot via coord_cartesian(xlim = ...).

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[Copilot]

plot_x_range/function_x_range start at 0. The control-limit functions produced by uprime_calculations() evaluate sqrt(cl / x) (see R/utils_plot.R:60), so sampling the function at x=0 yields Inf and can lead to warnings/incorrect rendering of the funnel control lines. Use a strictly positive lower bound for these x-limits (e.g., min_den <- min(rates_funnel_data$denominator[rates_funnel_data$denominator > 0]) or max(1, min_den)), and base the plot/function ranges off that instead of 0.

Suggested change

	plot_x_range <- c(0, max(rates_funnel_data$denominator) * 1.05)
	positive_denominators <- rates_funnel_data$denominator[rates_funnel_data$denominator > 0]
	min_den <- if (length(positive_denominators) &&
	is.finite(min(positive_denominators, na.rm = TRUE))) {
	min(positive_denominators, na.rm = TRUE)
	} else {
	1
	}
	max_den <- max(rates_funnel_data$denominator, na.rm = TRUE)
	if (!is.finite(max_den)) {
	max_den <- min_den
	}
	plot_x_range <- c(min_den, max_den * 1.05)

[Copilot]

function_x_range <- plot_x_range * 1.2 scales both the lower and upper bounds. If plot_x_range[1] is changed to a positive minimum (which is likely needed to avoid x=0 for the funnel functions), this will inadvertently increase the lower bound too. Prefer computing function_x_range by extending only the upper bound (keep the lower bound unchanged).

Suggested change

	function_x_range <- plot_x_range * 1.2
	function_x_range <- c(plot_x_range[1], plot_x_range[2] * 1.2)

[matt-dray]

Great, thanks for sticking this in.