more zsh fixes

more zsh fixes

- various comment updates
- moved some stuff out of zprofile and into zshenv for earlier use
- fixed zoxide bug until upstream fixes it
- PATH will now be updated twice, once in zshenv and once in zprofile
- rehash alias will update PATH before rehashing
- FPATH is now deduplicated like PATH is

Arch Linux and other systems (especially FreeBSD around version 10 and 11, last
I used it) do a lot of stuff to your shell environment via /etc/profile{,d},
and this may end up being sourced by the system zprofile for compatibility.
rather than shove everything into our local zprofile to override this aberrant
and often unwanted behavior as was previously done, let's just set things up in
zshenv as it should be, and if there are any problems, use load-site-dotfile
to fix things up instead. system profile scripts that make use of env vars will
also be taken care of with this approach, like flatpak-bindir.sh in the Arch
Linux flatpak package for example.

we also now update PATH twice so it can be set up early for our own purposes,
and so that any weird changes made by system profile scripts can be fixed.