fix: refactor the execution output logic using object-oriented approach

[chrisli30]

This pull request refactors the node output processing logic in core/taskengine/run_node_immediately.go to use a handler-based, object-oriented approach. The main goal is to eliminate code duplication, centralize output handling for different node types, and improve maintainability. Instead of using large switch statements, the code now delegates output extraction and protobuf conversion to specialized handlers.

Refactoring for handler-based node output processing:

• Replaced the large switch statement in extractExecutionResult with a handler-based approach using a NodeOutputHandlerFactory and node-specific handlers, which centralizes and simplifies output extraction for all node types.
• Added a new helper method detectNodeTypeFromStep to determine the node type from the execution step as a fallback when the type is not explicitly set.

Improvements to RPC response construction:

• Refactored error handling in RunNodeImmediatelyRPC to use handlers for creating empty output structures on failure, replacing the previous switch-based logic.
• Updated successful RPC response construction to use handlers for converting results to protobuf output, including proper metadata handling and special logic for contract write success determination.

Codebase cleanup:

• Removed legacy switch statements and redundant metadata extraction logic, consolidating all output and metadata handling into the new handler-based pattern.

Dependency management:

• Cleaned up unused imports related to legacy output processing utilities.

[Copilot]

Pull Request Overview

This PR refactors the execution output logic by introducing an object-oriented approach that replaces the large switch statements with a factory pattern and individual handler classes for each node type. This improves code maintainability and eliminates duplication in output processing logic.

Key changes:

• Introduces a NodeOutputHandler interface and factory pattern for managing different node types
• Replaces extensive switch statements with handler-based delegation in extractExecutionResult and RunNodeImmediatelyRPC
• Creates individual handler classes for each node type (RestAPI, CustomCode, Balance, etc.) in the new file

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
core/taskengine/run_node_immediately.go	Refactored to use handler-based approach, removed large switch statements, added node type detection fallback
core/taskengine/node_output_handlers.go	New file containing handler interface, factory, and individual handlers for each node type

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