Switch to `ggplot2::stat_ecdf()`?

This issue has no description.

The issue provides no files, tests, or entry points. Start by locating the package code that computes or plots empirical cumulative distribution functions, then review how that code currently works before assessing the `ggplot2::stat_ecdf()` alternative. Done means the relevant plots use the intended approach and existing behavior is covered by passing tests.

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