- Introduced `FlowInputRequestedEvent` and `FlowInputReceivedEvent` to manage user input requests and responses during flow execution.
- Added `InputProvider` protocol and `InputResponse` dataclass for customizable input handling.
- Enhanced `Flow` class with `ask()` method to request user input, including timeout handling and state checkpointing.
- Updated `FlowConfig` to support custom input providers.
- Created `input_provider.py` for default input provider implementations, including a console-based provider.
- Added comprehensive tests for `ask()` functionality, covering basic usage, timeout behavior, and integration with flow machinery.
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