Improve shell detection and add CLI argument validation

[dybdeskarphet]

Hey, sorry for the mess my formatter created. With this PR, script:

• Checks the file existence and validates CLI arguments in two different functions.
• Prints an error message if invalid arguments have passed.
• detect_history_file uses $SHELL environment variable if no arguments have passed.
• Checks if $ZDOTDIR exists for zsh shell.

[islemci]

Seems like it doesn't function as intended, have you tested the code on your device?

[dybdeskarphet]

Sorry, I accidentally deleted bash from the possible shells. It should work now.

[islemci]

Thank you for your contribution!