masonry_core: Add first-class pseudo-class state on WidgetState

[waywardmonkeys]

Motivation

Masonry tracks interaction states (hovered, active, focused, disabled) as individual booleans on WidgetState. When these change, the framework sets request_pre_paint and needs_paint, then calls widget.update(). But request_paint (for Widget::paint()) is not set by the framework— widgets must call ctx.request_paint_only() in their update() to get paint() re-run. This is fragile: every widget that changes appearance on hover/focus/active must remember to do this, and forgetting causes rendering bugs that are easy to miss.

There's also no unified state representation that a future style/selector system could match against. CSS-like selectors (:hover, :focus, :disabled, :checked) need a single queryable bitfield, not scattered booleans.

Changes

Introduce PseudoId(u8) and PseudoSet(u64) as a compact bitfield on WidgetState that mirrors the existing boolean interaction flags:

• Built-in pseudo IDs: HOVER(0), ACTIVE(1), FOCUS(2), FOCUS_WITHIN(3), DISABLED(4). Bits 5–63 are available for widget-defined states.
• Context API: ctx.set_pseudo(id, value) on mutable contexts auto-invalidates pre_paint + paint when state changes. ctx.pseudos() and ctx.has_pseudo(id) on all contexts for reads.
• Framework wiring: The update pass now sets pseudo bits alongside the existing boolean flags at all five interaction sites (hover, active, focus, focus-within, disabled). Also adds the missing request_paint = true at each site, fixing the root fragility.
• Widget-defined state: PSEUDO_TOGGLED(5) for checkboxes and switches. Checkbox::set_checked and Switch::set_on now use ctx.set_pseudo() instead of request_render(), and their update() methods no longer need manual request_paint_only() calls.

Next steps

• Style/selector matching: With pseudo state unified in a bitfield, a selector engine can match :hover, :active, :focus, :disabled, :checked etc. against widget_state.pseudos in a single bitmask comparison.
• Pseudo registry: A runtime registry for widget/app-defined pseudo IDs (allocating from bits 5+) so names can be used in stylesheets.
• Migrate remaining booleans: The existing is_hovered, is_active, etc. booleans could eventually be replaced by pseudo-set queries, reducing WidgetState size.
• Broader widget adoption: Other toggle-like widgets (disclosure panels, radio buttons) can adopt PSEUDO_TOGGLED or define their own pseudo states.

[waywardmonkeys]

@PoignardAzur This is a demonstration of what we talked about yesterday.

[waywardmonkeys]

This was calling request_render before, but now relies on what set_pseudo does, the accessibility (and a post-paint) are the missing bits. This widget doesn't need a post-paint.

[waywardmonkeys]

In the future, it would be up to the style engine to decide what needs requesting. This is just a step along the way.

[waywardmonkeys]

This is an example of doing it outside of PseudoId and would, in the future, be done with a registry. But not sure where to hang that registry from.