Add previousLogin method

[sammyskills]

Add a method to get the previous login record of a user, useful for displaying to the user, the last time the account was accessed.

[kenjis]

Can you add test code?

[kenjis]

You have a coding style violation.
Please run composer cs-fix to fix it.

   1) shield/tests/Unit/UserTest.php (no_whitespace_in_blank_line)
      ---------- begin diff ----------
--- /home/runner/work/shield/shield/tests/Unit/UserTest.php
+++ /home/runner/work/shield/shield/tests/Unit/UserTest.php
@@ -111,7 +111,7 @@
         // No logins found.
         $this->assertNull($this->user->previousLogin());
-        
+
         fake(
             LoginModel::class,
             ['id_type' => 'email', 'identifier' => $this->user->email, 'user_id' => $this->user->id]
      ----------- end diff -----------

[kenjis]

LGTM!