Add an interactive debug mode to protypyter, that accepts user input to prompt

[wenta0g]

This PR add a --interactive_debug flag that accepts user input to prompt. It is triggered when LLM's latest response fails to produce a valid fuzz target, after the initial prototyper prompt.
Usage:
./run_all_experiments.py --model=vertex_ai_gemini-1-5-chat -y ./benchmark-sets/comparison/igraph.yaml --agent --interactive_debug

This option can be used for prompt design and experiment, which is preferred to run independently from OSS-Fuzz-Gen's large-scale experiment. When the interactive mode is activated, the user can type in a prompt message from the terminal, following display like:

You may now enter a custom prompt for the LLM.
When finished:
Press Enter, then Ctrl+D (Linux/macOS)

The custom prompt is then wrapped into a prompt template to give more context to LLM

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