test: Add comprehensive edge case tests for ChatModel, ListOutputConverter, and ToolExecutionResult

[alxkm]

Summary

This PR adds comprehensive test coverage for three critical Spring AI components: ChatModel, ListOutputConverter, and ToolExecutionResult. The new tests focus on edge cases, error handling, and robustness scenarios that could occur in production AI applications.

Changes Made

ChatModelTests

• Exception propagation: Tests that exceptions from the underlying prompt call are properly propagated
• Null response handling: Verifies graceful handling when ChatResponse is null
• Null message handling: Tests behavior when AssistantMessage or its text content is null
• Multiline input processing: Ensures proper handling of input with various line ending formats
• State management: Validates that multiple calls to the same client work correctly

ListOutputConverterTest

• Complex CSV parsing: Tests handling of quoted values containing commas and newlines
• Mixed quoting styles: Validates behavior with single quotes, double quotes, and backticks
• Edge case inputs: Tests comma-only strings and malformed quoting scenarios
• Robustness validation: Ensures the converter doesn't crash on unexpected input formats

ToolExecutionResultTests

• Multiple tool response handling: Verifies that only the last ToolResponseMessage is processed
• Empty tool name validation: Tests behavior when tool names are empty strings
• Null tool ID handling: Ensures generations are still created when tool IDs are null
• Metadata integrity: Validates that tool metadata is properly preserved

Improvements

• Better Error Handling: Tests check how code handles missing data and null values
• Fewer Crashes: Tests prevent common errors that could break the application
• Safe Data Processing: Code handles bad input without throwing exceptions
• Future Protection: More tests help catch problems when making changes later
• Consistent Style: New tests match the existing test patterns in the project

[ilayaperumalg]

@alxkm Thanks for the PR improving the test coverage.