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/imagebam.py

@@ -63,8 +63,7 @@ class ImagebamGalleryExtractor(ImagebamExtractor):
             image.update(data)
             yield Message.Url, image["url"], image
 
-    @staticmethod
-    def metadata(page):
+    def metadata(self, page):
         return {"title": text.unescape(text.extr(
             page, 'id="gallery-name">', '<').strip())}