feat(readarr): render the edition details popup

Draw the edition details popup over the book details view. The popup body is
the scrollable text the book details handler builds from the already loaded
edition row, so it needs no tabs and no network call.

The text styling is extracted into a named function so both branches are unit
tested, and the shared test fixture now holds the real field lines instead of a
placeholder, which exercises the scroll offset and the values that themselves
contain a colon.

src/ui/readarr_ui/library/mod.rs

@@ -27,6 +27,7 @@ use crate::{
 
 mod author_details_ui;
 mod book_details_ui;
+mod edition_details_ui;
 
 #[cfg(test)]
 #[path = "library_ui_tests.rs"]