passExtensions.pass-import: convert to buildPythonApplication

Rewrite the derivation using buildPythonApplication, which makes the
wrappers a lot cleaner.
Adds tests because the application wasn't working as intended
due to the wrong file-magic python package (used "filemagic" instead of
desired "file-magic").

pkgs/tools/security/pass/extensions/default.nix

@@ -7,9 +7,7 @@ with pkgs;
     pythonPackages = python3Packages;
   };
   pass-checkup = callPackage ./checkup.nix {};
-  pass-import = callPackage ./import.nix {
-    pythonPackages = python3Packages;
-  };
+  pass-import = callPackage ./import.nix {};
   pass-otp = callPackage ./otp.nix {};
   pass-tomb = callPackage ./tomb.nix {};
   pass-update = callPackage ./update.nix {};