Call the record's boxes what they are

The offer names are from the protocol before this one, where a widget was
drawn twice and the record had to say which drawing was the question. It
is asked once now, so offer_part is the part it was asked in, offer_place
the place it was asked at, and place where its drawing was put: part,
asked and placed. LayoutHolds::frame is a range on the window since the
frame became a length of one, and the frame's own entry is the frame_len
pin beside it, so it is window; Painter::frame_own goes with it.
answers_at had one caller and said less than the line that replaces it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/cases/layout.rs

@@ -124,7 +124,7 @@ fn padding_keeps_the_frame_distinct_from_the_room_left_in_a_row() {
     h.set_root((icon, padded).span(Dir::RIGHT).width(rel(1.0)));
     let active = &h.render.active[&text.id()];
     let window = h.render.output_size().x;
-    let asked = active.offer_part.x.len().to_px(window);
+    let asked = active.part.x.len().to_px(window);
     assert_eq!(active.frame.x.to_px(window), Px::from_int(868));
     assert_eq!(asked, Px::from_int(844));
 }
@@ -171,7 +171,7 @@ fn padding_narrows_both_frame_and_box_inside_a_share() {
     let active = &h.render.active[&text.id()];
     let window = h.render.output_size().x;
     assert_eq!(active.frame.x.to_px(window), Px::from_int(418));
-    assert_eq!(active.offer_part.x.len().to_px(window), Px::from_int(418));
+    assert_eq!(active.part.x.len().to_px(window), Px::from_int(418));
 }
 
 #[test]