Provide completions for Nushell

[ysthakur]

This PR provides completions for z and zi. Nushell no longer uses external completers for internal commands since v0.103 (release notes), so people's old external Zoxide completers won't work anymore.

This completer uses the options completion_algorithm: "prefix", positional: false. positional was deprecated in 0.104 in favor of completion_algorithm: "substring". However, I chose not to use the substring algorithm because it won't work in older versions of Nushell. Also, this completer will probably end up being updated in a few Nushell releases anyway (some improvements to Nushell's completers are planned).

This completer also looks a little weird if you type in multiple arguments. If you type in z /foo bar<TAB>, all the completions you see will have everything up to and including the first /foo stripped. It's not great, but it's needed because custom completers in Nushell can't currently choose which span they want to replace. Without it, if your first result upon typing z /foo bar<TAB> were /foo/bar, hitting Enter would replace your command line with z /foo /foo/bar, which is incorrect.

[ysthakur]

@ajeetdsouza Could you take a look at this?

[azaleacolburn]

@ajeetdsouza This would be greatly appreciated.