Implement `<Slider>` tag (egui::Slider)

[ZhukMax]

Add a declarative <Slider> widget with a controlled numeric binding and range configuration. Support common UX options (label text, show value, vertical orientation, enable/disable, tooltip) and emit change events. Provide optional value quantization via step.

• A core numeric control for settings/preferences and live tweaking.
• Keeps templates concise while preserving a controlled-value model consistent with other EFx inputs.
• Reduces imperative boilerplate around egui sliders.

---

Scope

• Tag: <Slider>

• Required: value={number_expr}, and either min/max or range="a..=b".

• Optional attributes:

  • text="..." (label next to/inside the slider) or inline text children (mutually exclusive).
  • showValue=bool (display current value on the slider).
  • orientation="horizontal|vertical" (default: horizontal).
  • step=number (quantize the resulting value to multiples of step after drag).
  • enabled=bool, tooltip="...", id="...", width=f32, height=f32 (best-effort).

• Events:

  • onChange={|v| ...} — called when value changes.
  • onRelease={|v| ...} — optional; fires when the user releases the drag (based on Response::drag_released()).

Non-goals (here): custom value formatter, units/suffix, logarithmic scaling (can be proposed later if needed).

---

Proposed API (sketch)

Template

// Basic float slider with label text via attribute
efx!(ui, r#"
<Slider value={model.opacity} min="0.0" max="1.0" step="0.05"
        text="Opacity" showValue="true" onChange={|v| model.opacity = v}/>
"#);

// Vertical integer slider with inline label and release event
efx!(ui, r#"
<Slider value={model.quality} range="0..=100" orientation="vertical"
        onRelease={|v| save_quality(v)}>
  Quality
</Slider>
"#);

Conceptual mapping to egui

let mut v = /* bound number */;
let range = min..=max; // or parsed from "a..=b"
let mut s = egui::Slider::new(&mut v, range);

if let Some(label) = text_or_children_label { s = s.text(label); }
if show_value { s = s.show_value(true); }
if is_vertical { /* use vertical ctor or style hint if available */ }

let resp = if enabled { ui.add(s) } else { ui.add_enabled(false, s) };
if let Some(tip) = tooltip { resp.on_hover_text(tip); }

let mut v_out = v;
// Quantize if step is present
if let Some(step) = step_opt { v_out = quantize_to_step(v_out, step, min, max); }

let changed = resp.changed() && v_out != original_value;
if changed   { /* write back */ /* emit onChange(v_out) */ }
if resp.drag_released() { /* emit onRelease(v_out) */ }

---

Tasks

• AST & parsing

  • Add <Slider> node with attributes: value, min, max / range, text, showValue, orientation, step, enabled, tooltip, id, width, height.
  • Enforce single label source: children or text=... (error if both).
  • Validate range format (a..=b) and numeric types.

• Codegen

  • Bind value={expr} by copying into a local, pass &mut to egui::Slider, then write back if changed.
  • Map optional properties: label, showValue, enabled, tooltip, id, size hints.
  • Support vertical orientation using the appropriate egui API (vertical constructor or parameter).
  • Implement post-drag quantization for step (round to nearest multiple within [min, max]).
  • Emit onChange(v) when value changes; emit onRelease(v) when drag ends.

• Diagnostics

  • Missing value or min/max/range → clear error with expected usage.
  • Type mismatches (non-numeric value, mixed numeric types) → actionable message.
  • min > max or invalid range → compile error.
  • Dual label sources (children + text) → error; suggest picking one.
  • Unknown attributes → list allowed attributes for <Slider>.

• Examples & docs

  • examples/slider_basic.rs (float with step, showValue).
  • examples/slider_vertical.rs (integer, vertical, onRelease).
  • Cookbook snippet in docs/cookbook.md; entry in docs/tags.md.

• Tests

  • trybuild UI tests: missing/invalid attrs, wrong types, label conflict, bad ranges.
  • Unit test for quantization helper (step) and orientation mapping.
  • Ensure examples build for wasm32-unknown-unknown (no runtime).