Feat/hatched bar chart pattern

[ShashankSMayya]

This PR aims to add this feature #2008

Summary

Adds native, customizable hatch pattern (diagonal lines) support to ‎BarChartRodStackItem in FL Chart, allowing for visually distinctive stacked bar segments.

Main Changes

• New Properties:

▫ ‎isHatched and ‎hatchPattern on ‎BarChartRodStackItem for enabling and configuring hatching.
▫ ‎HatchPattern class supports color, background, angle, spacing, and stroke width.

• Rendering:

▫ Bar chart painter now draws hatch patterns with proper rounded clipping.

Examples & Tests:

▫ New ‎BarChartSample9 demonstrates hatching.
▫ Comprehensive tests for hatch pattern and stack item logic.

Usage

BarChartRodStackItem(
  fromY, toY, null,
  isHatched: true,
  hatchPattern: HatchPattern(
    hatchColor: Color(0xff38f3f3),
    backgroundColor: Color(0xff0293ee),
    spacing: 6.0,
    angle: -45.0,
    strokeWidth: 2.5,
  ),
)

Backwards compatible: Solid/gradient fills remain unchanged; hatching is opt-in.

Result

[imaNNeo]

Hi, thanks a lot for your contribution,
But someone is implementing it using shaders, so as it is more performant and expandable, I prefer to have that one #1958
I hope you understand the decision.