Add method to run any node with input variables

[devin-ai-integration]

Add method to run any node with input variables

This PR adds a method to run any node upon calling, with input variables provided as JSON key-value pairs. It validates required variables and returns the execution result.

Features

• Added method to the VM class to execute a single node with provided input variables
• Added helper method to create nodes of different types from simplified configuration
• Added high-level method to the Engine class for client usage
• Implemented comprehensive unit tests for the new functionality

Implementation Details

• The implementation is generalized to work with all node types, including triggers like blockTrigger
• For blockTrigger, it creates a custom code node that returns the block number
• The method respects that apContext variable contains secrets and should be read from the server-side
• Error handling is provided for missing required variables

Testing

• Added unit tests for different node types
• Tested with blockTrigger to get blockNumber response
• Verified error handling for missing variables

Link to Devin run: https://app.devin.ai/sessions/1db4b9cdbeea4d318c865f392ed87263
Requested by: Chris Li (chris@avaprotocol.org)

[devin-ai-integration]

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