Fish 3.2.0 is the minimum required version (#146)

Now that fish 3.2.0 has been out for almost a month, it's time to make it the minimum required version. Thankfully, the only new expectation made by the plugin is around the new set --show format. It has been simplified (see fish-shell/fish-shell#6944) such that the search shell variable preview logic, which uses set --show, can be greatly simplified. While this is technically backwards incompatible with fish 3.1.2, the only negative consequence for users who haven't upgraded should be that their variable preview won't be as clean and condensed but will still have all the essentials.

[Search directory] fix tilde in current token not expanding (83cb78f)

The bug happened when the current token is something like ~/Documents/ when executing search directory. It should have limited the search scope to ~/Documents but it didn't. Thankfully, the bug is now fixed. Thanks @kidonng for finding it!