Count duplicate originals once the sweep has dated them

A copy becomes a duplicate only once its capture time is read, and on a
fresh library that is the sweep, not the scan: the sidebar row stayed
hidden until the next launch. The count is refreshed when a sweep that
dated anything finishes.

Also says on a group left out of the plan that nothing will move, drops
an unused method, and names the review's completion callback type for
clippy.

ui/dr-ui/src/lib.rs

@@ -26,12 +26,12 @@ mod bursts;
 mod collections_ui;
 #[cfg(test)]
 mod decoder_seam;
-mod duplicates;
-mod duplicates_ui;
 mod derived_sync;
 mod develop;
 mod develop_ui;
 mod display_ui;
+mod duplicates;
+mod duplicates_ui;
 mod export;
 pub mod faces;
 pub use library::render_native;