Fix $env.PATH for direnv (#1083)

While using direnv with nushell, I noticed that my autocompletion for
external programs stopped working as soon as I entered a directory and
direnv loaded.

Turns out, direnv exports $PATH as a string, and nushell stores $PATH as
a table and expects it to be one. Worse, nu just silently fails any
operations with the $PATH (except for running programs) instead of
reporting an error.

This PR fixes that by adding a line in the direnv config.nu script that
parses that string into the appropriate table.
Testing it on my system (NixOS, nushell, direnv + lorri) it seems to
work perfectly fine and the $PATH works again.

nu-hooks/nu-hooks/direnv/config.nu

@@ -23,4 +23,8 @@
     }
 
     direnv export json | from json | default {} | load-env
+    # Direnv outputs $PATH as a string, but nushell silently breaks if isn't a list-like table.
+    # The following behemoth of Nu code turns this into nu's format while following the standards of how to handle quotes, use it if you need quote handling instead of the line below it:
+    # $env.PATH = $env.PATH | parse --regex ('' + `((?:(?:"(?:(?:\\[\\"])|.)*?")|(?:'.*?')|[^` + (char env_sep) + `]*)*)`) | each {|x| $x.capture0 | parse --regex `(?:"((?:(?:\\"|.))*?)")|(?:'(.*?)')|([^'"]*)` | each {|y| if ($y.capture0 != "") { $y.capture0 | str replace -ar `\\([\\"])` `$1` } else if ($y.capture1 != "") { $y.capture1 } else $y.capture2 } | str join }
+    $env.PATH = $env.PATH | split row (char env_sep)
 }