yazi: set default integration values for Nushell, Fish, and Zsh to true

[no-mood]

The programs.yazi.enableNushellIntegration, programs.yazi.enableFishIntegration, and programs.yazi.enableZshIntegration options were previously set to false by default.

I didn't find a clear convention, but most of the modules I reviewed set these options to true by default. Following this pattern, it seems more appropriate to enable these integrations by default to enhance the user experience.

Description

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC