gauge_kit v0.3.0

• GaugeAnnotation — new class for pinning arbitrary Flutter widgets at specific value
  positions around the RadialGauge arc. Supports radiusFraction and offset for
  precise placement.
• RadialGauge — converted to StatelessWidget wrapper supporting child (centre
  overlay), annotations (List<GaugeAnnotation>), labelFormatter (custom tick
  text), and unitText (centre value suffix).
• ArcGauge — converted to StatelessWidget wrapper with a full new layout tier:
  child (centre overlay), header / footer labels, fillColor (inner circle),
  widgetIndicator (moving tip widget), reverse (fill from far end), showValue,
  unitText, and backgroundWidth (override track stroke width).
• LinearGauge — converted to StatelessWidget wrapper with leading / trailing
  end widgets, center overlay, widgetIndicator (moving tip widget), reverse,
  showValue, unitText, labelFormatter, and barRadius (rounded filled-bar mode).
• Glow effects — GaugeTokens.valueGlowRadius (double, default 0.0) and
  GaugeTokens.valueGlowColor (Color?) added to all arc/linear render engines;
  positive radius renders a soft outer glow behind the value arc or bar.
• GaugeController.animateTo() — new onAnimationEnd callback fires when the
  animation completes.
• All new params are optional with sensible defaults — existing code requires zero
  changes.