Enable revive linter, and fix a bunch of warnings

I took the set of enabled checks from revive's recommended configuration [1],
and removed some that I didn't like. There might be other useful checks in
revive that we might want to enable, but this is a nice improvement already.

The bulk of the changes here are removing unnecessary else statements after
returns, but there are a few others too.

[1] https://github.com/mgechev/revive?tab=readme-ov-file#recommended-configuration

pkg/gui/keybindings/keybindings.go

@@ -41,9 +41,8 @@ func GetKey(key string) types.Key {
 		binding, ok := config.KeyByLabel[strings.ToLower(key)]
 		if !ok {
 			log.Fatalf("Unrecognized key %s for keybinding. For permitted values see %s", strings.ToLower(key), constants.Links.Docs.CustomKeybindings)
-		} else {
-			return binding
 		}
+		return binding
 	} else if runeCount == 1 {
 		return []rune(key)[0]
 	}