Refresh background color preview on HSV slider changes and refactor HSVSliderGroup

[beackers]

Motivation

• Make the background color preview in flow_field.xml update live when the bg HSV sliders are moved.
• Provide a mechanism for grouped slider handlers to receive combined HSV updates.
• Keep slider bindings flexible so external listeners can react to progress changes.

Description

• Add a ProgressCallback interface and optional callback support to SliderBinding via a new constructor and setProgressCallback, and invoke it from onProgressChanged in the slider listener.
• Wire the same callback invocation into LogSliderBinding so logarithmic sliders can also trigger external listeners.
• Refactor HSVSliderGroup to accept an HSVChangeListener, store individual SliderBinding instances, register per-slider ProgressCallbacks that compute combined HSV with getValue, and call the HSVChangeListener on changes.
• Update FlowFieldActivity to pass a lambda to HSVSliderGroup that calls a new updateBgColorPreview helper which sets the bgColorPreview background with Color.HSVToColor, and add the necessary import.

Testing

• No automated tests were run for this change.

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