Let a rule beat a hint, and name marking a widget for redraw

A ninth sweep, over the part no earlier round named -- the widget vocabulary and
the builder methods, `Widgets`, the examples, the `util` additions and the
manifests -- and once more over `77ed7a2`, the eighth sweep's own commit and so
itself unreviewed.

A hint overrode a rule. `declared_lens` asked `rules[axis].declared()` first and
fell through to the widget's own `size_hint` whenever that answered `None` --
which it does for a share, since a share is not a declaration. So a widget
carrying `width(leftover(1))` and hinting a pixel length of its own was handed a
box of the hint, against the rule and against the comment inside the function:
"a hint still narrows the box where no rule does". `Painter::size_hint` spells
the same rule-else-hint step three hundred lines up and gets it right, with the
reason written on it; both read `Widgets::exact_len` now, and `declared_lens` is
the part of its answer that needs nobody to divide it. `Image` is the only
widget here whose hint is a declared length, and neither the tests nor the
generator builds one, so nothing in this repository could reach the difference
-- which is why the dump is unchanged and why the test builds a widget of its
own. It records the box it was asked in: 400 with the rule and 50 without, and
50 either way before this.

Marking a widget for redraw had no name. Twenty-one sites under `tests/` said it
as `widgets_mut().get_dyn_mut(id);` with the widget thrown away, five with a
`let _ =` in front, one with a comment explaining what the line was for, and one
wrapped in a local function called `mark`. `Widgets::mark_for_redraw` says it.
`revision_cost.rs` keeps the long spelling and now says why in place: it is
deliberately in the API subset an old worktree also has.

`assert_same_regions` could not see the defect the eighth sweep had just fixed.
It zips the warm and cold id lists, so a list naming one widget twice -- which
is what `width`, `sized` and `align` giving back their own argument produces --
compares fewer boxes than it lists and says nothing about it. It now rejects a
repeated id and two lists of different lengths, which also checks the nine
fixtures that round left alone: all eighteen cases pass.

Bare pairs where the framework has named ones. `random.rs`'s `Lens` and `Aligns`
were `[Option<LayoutLen>; 2]` and `[Option<AxisAlign>; 2]`, read as `[0]`/`[1]`
and zipped against a hand-written `[Axis::X, Axis::Y]`. They are `SizeRules` and
`Align`; `Align` took the `Index<Axis>` every other per-axis pair on this branch
has, and `RegionAlign::from` does the "an axis left out is centred" step two
rigs were spelling per axis. The three sites that wrote the axis pair out say
`Axis::BOTH`, which is what the rest of the layout code says.

`BothAxis<T>`, `AxisT`, `XAxis` and `YAxis` -- 45 lines with a const trait, two
marker types and three accessors -- have no user anywhere in the workspace. They
are the mechanism `impl_axis_index!` replaced, in the file this branch took
`Vec2::axis`/`axis_mut` out of. Deleted, which is a drive-by in a block the
branch was already rewriting; drop it if the scope matters more.

Smaller things, each in its own place: `Wrapper` arrived beside core's
`WidgetWrapper`, one word for a widget that wraps a child and for a dynamic
borrow guard, so the alias is gone and its two uses name `DynBorrower` -- which
is what they are. `Wrapper::new`, `Wrapper::empty` and its `Default` were three
names for one value, two of them unused. `Arena::get_mut` was the only
`pub(crate)` among `pub` siblings on a public type. `Selector` rounded the
pointer onto the pixel grid to do arithmetic on two values already there, losing
the precision the platform gave it for nothing; the step between the regions is
taken on the grid instead. And the two `debug` profile settings carry their
reason where the next reader looks rather than only in the commit that made
them, one of which was about renaming `rest`.

Format, clippy with and without layout-diagnostics, and the suite (132 + 19 + 13
+ 4) are clean. The cold dump over 400 depth-5 trees is byte-identical to
`77ed7a2` across all 34,488 boxes, and all three seed scans pass: 400 at depth 5
in 63.27s, 1,000 at depth 6 in 160.45s, 2,000 at depth 4 in 302.52s.

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

src/widget/trait_fns.rs

@@ -19,8 +19,8 @@ widget_trait! {
         move |state| {
             let id = self.add(state);
             let widgets = &mut state.ui_mut().widgets;
-            for (axis, align) in [(Axis::X, align.x), (Axis::Y, align.y)] {
-                if let Some(align) = align {
+            for axis in Axis::BOTH {
+                if let Some(align) = align[axis] {
                     widgets.set_alignment(id, axis, align);
                 }
             }

src/widget/wrapper.rs

@@ -9,6 +9,7 @@ use std::marker::Unsize;
 ///
 /// Its child is optional so it can also be the swappable slot a tab bar
 /// needs, which is what it was written for.
+#[derive(Default)]
 pub struct Wrapper {
     pub inner: Option<StrongWidget>,
 }
@@ -26,11 +27,7 @@ impl Wrapper {
     pub fn new() -> Self {
         Self::default()
     }
-    pub fn empty() -> Self {
-        Self {
-            inner: Default::default(),
-        }
-    }
+
     pub fn set<W: ?Sized + Unsize<dyn Widget>>(&mut self, to: StrongWidget<W>) {
         self.inner = Some(to)
     }
@@ -42,9 +39,3 @@ impl Wrapper {
         self.inner.replace(to)
     }
 }
-
-impl Default for Wrapper {
-    fn default() -> Self {
-        Self::empty()
-    }
-}