apex_dropdown

• Feature: Implement ApexAsyncDropdown<T> (real async overlay with debounce, last-query-wins, caching, and loading/error/empty states).
• Feature: Add ApexAsyncMultiDropdown<T> + ApexAsyncMultiDropdownFormField<T>.
• UI: Multi-select count mode now shows "N selected" even when the field has a fixed height.
• Example: Add async single + multi dropdown demos to the example app.

• UI: Reduce the default closed-field height from 48 → 46 (applies to dropdown widgets and their FormField variants).
• API: Make itemLabel optional across dropdowns and form fields; defaults to toString() for model types (and safely renders '' for null items).
• Docs: Improve public API documentation coverage (adds missing DartDoc for apex_dropdown exports and ApexAsyncDropdown members).

Initial release of apex_dropdown.

• ApexDropdown<T> (single select): controllerless dropdown with a route-safe overlay.
• Model support: itemLabel (required) + compareFn for identity matching (e.g. compare by ID).
• Crash-proof mismatches: never throws if value is not present in items; shows hintText instead and logs debug warnings (optionally calls onInvalidValue in debug).
• Local search: searchEnabled with default case-insensitive contains, plus searchMatcher for custom filtering.
• Lifecycle safety: overlay is removed on dispose() and dismissed on route pop (prevents setState-after-dispose / orphaned overlays).

Notes:

• ApexAsyncDropdown<T> is exported for API stability but currently renders placeholder UI while the full async implementation is in progress.