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.

gallery_dl/extractor/philomena.py

@@ -35,8 +35,7 @@ class PhilomenaExtractor(BooruExtractor):
             return url.rpartition(".")[0] + ".svg"
         return url
 
-    @staticmethod
-    def _prepare(post):
+    def _prepare(self, post):
         post["date"] = text.parse_datetime(
             post["created_at"][:19], "%Y-%m-%dT%H:%M:%S")