Add support for optional parameters in @Annotations.Schema

[jinnigu]

Add optional parameter to @Annotations.Schema to mark function parameters as optional, excluding them from the "required" array in generated function schemas.

// Example func
public Map<String, Object> executeExample(
    @Annotations.Schema(name = "requiredParam", description = "A required parameter") 
    String requiredParam,
    
    @Annotations.Schema(name = "optionalParam", description = "An optional parameter", optional = true)
    Integer optionalParam
) {
    // implementation
}

// Generated schema
{
  "required": ["requiredParam"]
}

Fix #493

[gemini-code-assist]

Summary of Changes

Hello @jinnigu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant enhancement by enabling the definition of optional parameters within function schemas. By adding an optional flag to the @Annotations.Schema annotation, developers can now explicitly mark function arguments as non-mandatory. This change ensures that generated function schemas accurately reflect which parameters are truly required, and during function execution, missing optional arguments are handled by passing null instead of throwing an error, improving flexibility and robustness in function calling.

Highlights

• Annotation Extension: The @Annotations.Schema annotation now includes an optional boolean parameter, defaulting to false, allowing explicit marking of optional function arguments.
• Schema Generation Update: The FunctionCallingUtils class has been updated to exclude parameters marked as optional=true from the required array when generating function schemas.
• Runtime Handling of Optional Parameters: The FunctionTool class now gracefully handles missing optional parameters during function invocation by passing null for them, preventing IllegalArgumentException for non-mandatory arguments.
• Comprehensive Testing: New unit tests have been added to FunctionToolTest to validate that optional parameters are correctly excluded from schema requirements and handled appropriately during function calls.

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[gemini-code-assist]

Code Review

This pull request adds support for optional parameters in @Annotations.Schema. The changes are well-implemented across the annotation definition, schema building logic, and function invocation. I've provided a couple of suggestions to improve code readability, efficiency, and reduce duplication in FunctionTool and FunctionCallingUtils. The added tests are comprehensive and cover the new functionality well.