feat: Implement child workflow core functionality

[daryllimyt]

Features

• Implement basic child workflow invocation
• Add event history for child workflows + UI
• Implement looping for child workflows
  • Child workflow loops run at the temporal workflow level
  • Udfs still run loop iteration inside the temporal activity
• Implement all and isolated fail strategies using asyncio.gather / GatheringTaskGroup
• Implement parallel, sequential, and batched loop strategies
• Implement returns key for DSLInput. Pass an expression to define the return value of the workflow.

Changes

• Break workflow/service.py into workflow/definitions.py and workflow/executions.py
• Refator some models to avoid circular imports
• Standardize colors to avoid confusion

Testing

• Added new workflow test

Example usage

title: Parent workflow
description: Test child workflow
entrypoint:
  ref: parent
inputs:
  data: [1, 2, 3, 4, 5, 6, 7]

actions:
  - ref: parent
    for_each: ${{ for var.x in INPUTS.data }}
    action: core.workflow.execute
    args:
      workflow_id: <<child workflow id>>
      loop_strategy: parallel
      fail_strategy: isolated
      batch_size: 3
      trigger_inputs:
        number: ${{ var.x }}

Todos

• Missing subsytem to register workflows as executables, which will enable referencing workflows using unique refs instead of IDs.