feat(treemap): Add rebuildToken parameter to support data value updates

[AcarFurkan]

Problem

SfTreemap doesn't update when data values change if dataCount stays the same.

FR: https://www.syncfusion.com/feedback/47083/provide-dynamic-update-support-for-treemap-datasource-without-changing-the-data

Previous Workaround

The only way to force a rebuild was using a Key:

SfTreemap(
  key: ValueKey(Object.hashAll(data.map((e) => e.hashCode))),
  dataCount: data.length,
  // ...
)

Downsides:
- Forces complete widget rebuild (loses state, animations)
- Not intuitive - key is meant for widget identity, not data changes

Solution

Added optional rebuildToken parameter. When this value changes, the widget rebuilds
even if dataCount is unchanged.

SfTreemap(
  dataCount: data.length,
  rebuildToken: Object.hashAll(data.map((e) => e.hashCode)),
  // ...
)

Or simply use an int counter:

int _rebuildCounter = 0;

// When data changes:
setState(() {
  _rebuildCounter++;
});

SfTreemap(
  dataCount: data.length,
  rebuildToken: _rebuildCounter,
  // ...
)

Advantages:
- Clean, declarative API
- Explicit intent - clearly indicates "rebuild when data changes"
- No breaking changes - parameter is optional with default null

Demo

Before (no update):

before.mov

After (with rebuildToken):

UPDATED.mov

Fixes #1396