[PLT-3337] SDK - Workflow Management allow multiple inputs

[paulnoirel]

Format updated by linter

Description

In the SDK, remove a limitation in workflow management so nodes can accept multiple inputs from different nodes, and not just from initial nodes.

Tests:

1. In the Labelbox platform, create a new project

2. For 1. change the workflow like the following:

   

3. Create a second project

4. From the SDK, update the values and run the following scripts:

   import labelbox as lb
   
   # Values to update
   API_KEY = "<your API KEY>"
   SOURCE_PROJECT_ID = "<project ID from 1.>"
   TARGET_PROJECT_ID = "<project ID from 2.>"
   
   client = lb.Client(API_KEY)
   target_project = client.get_project(TARGET_PROJECT_ID)
   
   # The following must be successful if SOURCE_PROJECT_ID is a project with a valid workflow
   target_project.clone_from_project(SOURCE_PROJECT_ID)

Fixes PLT-3337

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Document change (fix typo or modifying any markdown files, code comments or anything in the examples folder only)

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Changes to Core Features

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Note

Enables multi-input nodes from any predecessors by relaxing validation rules.

• Updates WorkflowValidator.validate_node_connections to remove the check that all predecessors must be initial nodes; still enforces at least one incoming for non-initial and at least one outgoing for non-terminal nodes
• Adds integration test test_workflow_allows_multiple_incoming_from_non_initial_nodes in tests/integration/test_workflow.py
• Adds unit tests in tests/unit/test_workflow_utils_validation.py to verify multiple incoming from non-initial nodes is allowed and that missing incoming connections are still flagged

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