feat(pack): add nushell language pack

[cfbender]

Closes #1594

📑 Description

Adds the nushell language pack

ℹ Additional Information

Wasn't 100% sure if conform installs it's own nufmt, but I was pretty sure it doesn't - so I put it in the readme as needing a local install.

[github-actions]

Review Checklist

Does this PR follow the [Contribution Guidelines](development guidelines)? Following is a partial checklist:

Proper conventional commit scoping:

• If you are adding a new plugin, the scope would be the name of the category it is being added into. ex. feat(utility): added noice.nvim plugin

• If you are modifying a pre-existing plugin or pack, the scope would be the name of the plugin folder. ex. fix(noice-nvim): fix LSP handler error

• Pull request title has the appropriate conventional commit type and scope where the scope is the name of the pre-existing directory in the project as described above

• README is properly formatted and uses fenced in links with <url> unless they are inside a [title](url)

• Entry returns a single plugin spec with the new plugin as the only top level spec (not applicable for recipes or packs).

• Proper usage of opts table rather than setting things up with the config function.

• Proper usage of specs table for all specs that are not dependencies of a given plugin (not applicable for recipes or packs).

[azdanov]

You're correct that it needs to be manually installed. Mason doesn't seem to have nufmt, and conform doesn't install dependencies, only sets up formatting capabilities.

[azdanov]

Also, would be good to mention that nushell itself is a requirement, since lsp won't work without it.

[azdanov]

LGTM, thanks!