DChartBlock is incomplete and currently unused

[RiadhCherni]

The DChartBlock class exists as a DBlock specialization:

open class DChartBlock(parent: DForm, model: VBlock)
    : DBlock(parent, model), BlockListener

However, it is currently incomplete and not used anywhere in the framework.

Unlike the other Block implementations (DBlock, DFullCalendarBlock, DGridBlock, DGridMultiBlock), this class:

• Does not provide a complete chart implementation
• Is not integrated in the block creation flow
• Lacks clear functional definition

This creates architectural ambiguity and unnecessary maintenance overhead.

Proposed action:
Complete the implementation of DChartBlock:

• Define its expected behavior.
• Implement missing features.
• Integrate it into the block creation flow.
• Add documentation and examples.