feat: Extract shell command from backticks

[Columpio]

What is done?

A produced command is extracted from markdown backticks in --shell mode

Why?

Because LLMs are usually taught to produce markdown output. So, even if you ask gently in a prompt, you get markdown backticks most of the time. You will get it especially often on small models, e.g., when running Ollama.

What I tested

• If LLM generates no backticks, it's output is returned as is
• LLM generates multiline command
• LLM generates a command which itself contains backticks for some reason (e.g., you ask to grep -rnI "```")
• LLM generates a surrounding comment text with backticks
• Windows/Linux/Mac-style newlines

P.S.

Hope other Ollama guys like me will now be happy. Please like this PR if you are.

With this PR I can finally do DEFAULT_MODEL=ollama/qwen2.5-coder:3b-instruct-q6_K.