Add unit tests to test new feat. X detection regex

The previous version of the `plugins.feat_tokens` regular expression
only matched "feat. X" parts if preceded by a space. This caused missed
detections in the `ftintitle.contains_feat` function.
This commit adds unit tests for the updated regex that also matches
"feat. X" parts within parentheses and brackets

test/plugins/test_ftintitle.py

@@ -183,5 +183,10 @@ def test_contains_feat(self):
         assert ftintitle.contains_feat("Alice & Bob")
         assert ftintitle.contains_feat("Alice and Bob")
         assert ftintitle.contains_feat("Alice With Bob")
+        assert ftintitle.contains_feat("Alice (ft. Bob)")
+        assert ftintitle.contains_feat("Alice (feat. Bob)")
+        assert ftintitle.contains_feat("Alice [ft. Bob]")
+        assert ftintitle.contains_feat("Alice [feat. Bob]")
         assert not ftintitle.contains_feat("Alice defeat Bob")
         assert not ftintitle.contains_feat("Aliceft.Bob")
+        assert not ftintitle.contains_feat("Alice (defeat Bob)")