MAJOR new features

[Search git status] preview changed files (#237, @NextAlone)

Show a preview of the unstaged and staged changes of the hovered-over file. This will make it easier to identify which files to select and perhaps offer a faster-to-navigate alternative to git diff.

[Search git log] include diff stats in preview (#238, @NextAlone)

Include diff stats when previewing commits to provide a quick overview of the files changed, which will be very helpful when the diff is very large and involves multiple files.

Behind the scenes changes

[Search directory] Prevent duplicate / when fd version >= 8.4.0 (#241, @kidonng)

fd 8.4.0 contains this change: "Directories are now printed with an additional path separator at the end".
fzf.fish has another feature that appends / for quick cds. This causes a duplicate / at the end that is confusing and looks terrible, though it may not actually cause issues. We fix this by preventing the / to be appended when the fd version is >= 8.4.0.

[Search variables] Always wrap preview (#239, @jaminthorns)

Useful for when the variable is very long, e.g. database URI. There shouldn't be any situation in which this is an inconvenience.

BIG thanks to @NextAlone for working hard and patiently with me on #237 to get it merged. It was the third PR to attempt this change, which shows how difficult it is to design well from a product standpoint. But NextAlone did it!