Add --fix option to correct the last command (#698)

[demouo]

Hi! Backgroud and motivation from #698

When I got an error command, I would like to correct ai that the command ... was wrong with the output ..., please fix it.

example follows:

This PR introduces a --fix flag. When used, sgpt retrieves the last executed command and its output, then prompts the AI to provide a corrected version based on the error.

Key changes:

• Added --fix option to sgpt/app.py.
• Created sgpt/command.py to manage storing and retrieving the last command and output in json format.
• Updated sgpt/utils.py to set and get the last command.
• Replaced os.system with subprocess.Popen in run_command to capture output.
• Added get_fixed_prompt to generate the prompt for the AI.
• Store command and output using the new Command class.
• Updated tests in tests/test_shell.py to reflect the use of subprocess.
• Added necessary configuration in sgpt/config.py.

make sure the lint and test result as usual:

Closes #698

[demouo]

The 2nd~4th Commits' changes:

1. LLM sometimes could not completely return the pure shell code, so I wrote the extracting function

2. Due to I was not familiar with the operation, I accidentally wrote several empty prompts, which should be ended before chatting with LLM

3. The idea of fix last command was added in REPL mode.

Hope everything goes well!