fix: correct ChainedInvokeDetails key in from_dict

[alessandrobologna]

Summary

• Fix incorrect key name in Operation.from_dict() that caused invoke() to return None
• Changed key from snake_case "chained_invoke_details" to PascalCase "ChainedInvokeDetails" to match API response format
• Added missing assertions in test_operation_from_dict_complete to prevent regression

Root Cause

In src/aws_durable_execution_sdk_python/lambda_service.py at line 752, the deserialization method used "chained_invoke_details" (snake_case) instead
of "ChainedInvokeDetails" (PascalCase), which is inconsistent with:

1. Other detail fields that correctly use PascalCase: "StepDetails", "WaitDetails", "CallbackDetails"
2. The corresponding to_dict() method which correctly uses "ChainedInvokeDetails"
3. The API response format

Test plan

• All existing tests pass (924 tests)
• Coverage maintained at 98.67% (above required 98%)
• Added assertion to verify chained_invoke_details is properly deserialized
• Linting passes (ruff check and ruff format --check on changed files)

Fixes #237

[alessandrobologna]

Closing and re-opening due to wrong format for the title

[yaythomas]

[yaythomas]

Thank you so much @alessandrobologna! 🙌