Puffer Card v1.2.3

Fixed

• White flash on the chart every ~60 seconds during periodic data refresh.
  _histLoading was a Lit reactive property, so setting it to true at the
  start of every fetch triggered a full re-render that momentarily replaced
  the chart with the loading placeholder — visible as a white flash.
  Fix: _histLoading is no longer a reactive property; re-renders are
  triggered manually via requestUpdate() only when data actually arrives.
  The loading placeholder is shown only during the very first fetch (when
  no history data exists yet); subsequent silent refreshes keep the existing
  chart visible until new data is ready.