fix(graph): fixes bug that caused simple flows with Loop to fail (#8809)

* fix: improve predecessors check for loop component

- Enhanced the handling of cycle vertices to prevent infinite loops by ensuring that a vertex can only run if all pending predecessors have completed.
- Updated conditions for the first execution of cycle vertices to allow running only if all pending predecessors are also cycle vertices.
- This refactor improves the robustness of the vertex management system in asynchronous workflows.

* fix: update _mark_branch method to return visited vertices and refine predecessor mapping

* fix: prevent duplicate item dependencies in LoopComponent

* feat: add loop connection handling in Component class

- Introduced methods to process loop feedback connections, allowing components to connect outputs to loop-enabled inputs.
- Implemented checks to validate loop connections and ensure proper handling of callable methods from other components.
- Enhanced the edge creation logic to support special loop feedback edges targeting outputs instead of inputs.

* fix: enhance name overlap validation in FrontendNode

- Updated the validate_name_overlap method to exclude outputs that allow loops from the overlap check.
- Improved error message to include the display name of the component, along with detailed lists of input and output names for better debugging.

* fix: correct condition for executing cycle vertices in RunnableVerticesManager

- Updated the logic to ensure that a cycle vertex can only execute if it is a loop and all pending predecessors are cycle vertices. This change enhances the robustness of the vertex management system in asynchronous workflows.

* feat: implement comprehensive loop flow for URL processing

- Added a new loop flow that processes multiple URLs through a series of components including URLComponent, SplitTextComponent, LoopComponent, ParserComponent, PromptComponent, OpenAIModelComponent, StructuredOutputComponent, and ChatOutput.
- Enhanced the StructuredOutputComponent to include a detailed system prompt and refined output schema to ensure proper JSON formatting.
- Introduced a test case to validate the creation and execution of the loop flow, ensuring all components are correctly integrated and the expected execution order is maintained.

* refactor: enhance loop target handling in Component and Edge classes

- Introduced LoopTargetHandleDict to better manage loop target structures in the Component and Edge classes.
- Updated the Component class to utilize type casting for loop target handles, improving type safety.
- Refactored the Edge class to accommodate the new loop target handling, ensuring compatibility with existing edge structures.
- Removed deprecated message handling methods from the Component class to streamline the codebase and improve maintainability.

* test: skip OpenAI model integration test if API key is not set

- Added a conditional skip to the test_build_model_integration_reasoning method to prevent execution when the OPENAI_API_KEY environment variable is not set, ensuring tests run only in appropriate environments.

* [autofix.ci] apply automated fixes

* chore: add required secrets for OpenAI and Anthropic APIs in CI workflows

* Updated ci.yml to include OPENAI_API_KEY and ANTHROPIC_API_KEY secrets.
* Modified python_test.yml to mark these secrets as required for workflow execution.

* fix: update OPENAI_API_KEY check in test_loop.py to handle dummy values

* Modified the condition in the pytest skipif decorator to also skip tests when OPENAI_API_KEY is set to "dummy", ensuring more robust test execution.

* refactor: streamline component setup in test_loop.py

* Removed redundant comments and improved formatting for component initialization in the loop_flow function.
* Added missing system_prompt to StructuredOutputComponent to resolve "Multiple structured outputs" error.
* Updated test_loop_flow to ensure it tests the graph creation with proper loop feedback connection.

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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>