Implement invoke operation

[yaythomas]

Context

Replace temporary method implementation with full invoke logic

Technical Requirements

• Replace temporary method implementation with full invoke logic
• Add proper function execution and result handling
• Implement operation status transitions (SUCCEEDED/FAILED)
• Add parameter validation and error handling
• Add ResourceNotFoundException for non-existent functions

Implementation Details

• File: src/aws_durable_execution_sdk_python_testing/invoker.py:137

Acceptance Criteria

• Temporary method implementation replaced with full invoke logic
• Proper function execution and result handling added
• Operation status transitions implemented (SUCCEEDED/FAILED)
• Parameter validation and error handling added
• ResourceNotFoundException added for non-existent functions