Ask each child once and place its answer by re-expression

A widget draws in the box it is asked in and its answer is placed inside
that box by re-expressing the drawing; nothing is drawn again in a box an
answer chose. The offer machinery, whose job was to tell a measuring draw
from a placing one, goes with the placing draw. A span measures each child
from its cursor and moves fixed children to their slots with place_at; a
share child is asked once more in its decided slot with its frame narrowed
to it. A stack asks non-sizing children in the box its sizing child
decided. A scroll asks its content once and moves it to the scrolled
offset. A local redraw asks the retained question again and puts the
answer back where the parent placed it.

A symbolic length a child pinned composes through Part::Of exactly where
the part is the whole box less pixels, and pins the parent's own length
otherwise; dropping it let a pad reuse a drawing across a narrowed frame
of the same pixel length (shrinker seeds 60, 248 and 384 at depth 5).

Suite 114/114 including the two decided-box pins, fast oracle 11/11,
shrinker 400 seeds at depth 5 over all fifteen cases.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

core/src/layout_diagnostics.rs

@@ -32,7 +32,6 @@ pub(crate) enum Counter {
     SizeReads,
     HintHits,
     HintMisses,
-    RetainedSizeHits,
     ReuseAttempts,
     ReuseExact,
     ReuseMoved,
@@ -42,7 +41,6 @@ pub(crate) enum Counter {
     ReuseOutside,
     ReuseWrongLayer,
     ReuseWrongNode,
-    PlaceRedraws,
     QueuePops,
     DepthReads,
     LocalRedraws,
@@ -70,7 +68,6 @@ impl Counter {
         "draw-result size reads",
         "hint hits",
         "hint misses",
-        "retained size hits",
         "reuse attempts",
         "reuse exact",
         "reuse moved",
@@ -80,7 +77,6 @@ impl Counter {
         "reuse: outside what it holds for",
         "reuse: another layer",
         "reuse: region-node choice changed",
-        "placed by redrawing",
         "redraw queue pops",
         "depth reads",
         "local redraws",