remove @staticmethod decorators

There might have been a time when calling a static method was faster
than a regular method, but that is no longer the case. According to
micro-benchmarks, it is 70% slower in CPython 3.13 and it also makes
executing the code of a class definition slower.

test/test_extractor.py

@@ -296,8 +296,7 @@ class TestExtractorWait(unittest.TestCase):
         u = self._isotime_to_seconds(until.time().isoformat()[:8])
         self.assertLessEqual(o-u, 1.0)
 
-    @staticmethod
-    def _isotime_to_seconds(isotime):
+    def _isotime_to_seconds(self, isotime):
         parts = isotime.split(":")
         return int(parts[0]) * 3600 + int(parts[1]) * 60 + int(parts[2])