Initialize McFly only in interactive shell

[akinomyoga]

In the current setup for Bash and Fish, only keybindings are disabled in non-interactive shells, but the other settings (including PROMPT_COMMAND, MCFLY_SESSION_ID, etc.) are still loaded. Do they need to be loaded in the non-interactive shells? On the other hand, in the Zsh setup, they are not enabled in non-interactive shells because there is a check [[ -o interactive ]] at the beginning of mcfly.zsh (though there is an extra check for the interactive shell also for the keybindings in Zsh).

In this PR, I suggest skipping all the initialization in non-interactive shells to make it consistent with Zsh, which I guess is the natural behavior. I also remove the redundant check for the interactive shells in the later part of the Zsh integration.

If these settings (other than keybindings) are intentionally enabled in non-interactive shells of Bash and Fish, please let me know. I can adjust or close the PR. Thank you.

[cantino]

Thanks @akinomyoga!

[akinomyoga]

Thanks! I'll submit other PRs (I waited for this PR to avoid unnecessary conflicts caused by the merging order).

In case you missed it, I replied to your email at around 21:25 on Thu, 11 Jul 2024 (PDT).