This PR introduces the Workflow Builder for API Dash as a Proof of Concept, including both the visual design and the initial version of the execution engine.

Previously, in PR #817, I submitted the Collection Runner and Performance Load Testing features. As mentioned in the comments on that PR, I was working on the workflow builder canvas — this update delivers that feature with basic execution capabilities.

What’s Included in This PR:
Visual Workflow Canvas: A drag-and-drop interface that allows users to design multi-step API workflows by placing and connecting nodes.

Node Types Supported:

Start – defines the beginning of a workflow
Request – makes an API call
Condition – adds branching logic
Transform – performs simple data manipulation

Connection Management: Users can connect nodes based on flow outcomes (success, error, condition).

Bidirectional Sync: All changes to the visual interface sync with the underlying workflow model and vice versa.

Execution Engine (Initial Version):

Allows step-by-step execution of workflows
Provides visual feedback as each node executes
Supports execution state tracking and basic error handling
Architecture: Built with a clean separation between UI and execution logic, making the system extensible and maintainable.

The visual component uses the flutter_flow_chart package for rendering, while the custom engine handles the execution flow logic.

Future Enhancement/Plans:
Add display block in canvas (text,chart etc)
Support for nested workflows and reusable subflows
Enable grouping of related nodes for better visual clarity
Add dynamic data flow and node-level configuration

Related Issues:

Checklist:
✅ Followed the contributing guide

✅ Synced with the latest main branch

✅ Using the latest Flutter stable version

✅ All tests passing (flutter test)

Tests Added or Updated?
✅ No

Tested On:
macOS