- Fix caller-owned LoadSwitchController left loading forever when a
  controlled switch was disposed, changed mode, or swapped mid-toggle
- Fix managed switch stranded loading after isLoading returned to default
- SpinStyle.cupertino now honors spinColor; waveSpinner renders
  SpinKitWaveSpinner
- Directional thumb alignment for RTL, keyboard-reachable inactive
  switches, focus indicator, focusNode/autofocus/focusColor and
  configurable semantic hints
- Stricter constructor assertions for dimensions, stroke width and
  animation durations
- Test suite 23 -> 47; core library at 100% line coverage