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 https://github.com/fish-shell/fish-shell/issues/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.