Replace pkg_resources with importlib.resources for Python 3.14 compatibility

ebook_converter/ebooks/oeb/stylizer.py

@@ -2,7 +2,7 @@
 CSS property propagation class.
 """
 import os, re, logging, copy, unicodedata, numbers
-import pkg_resources
+from importlib.resources import files
 from operator import itemgetter
 from weakref import WeakKeyDictionary
 from xml.dom import SyntaxErr as CSSSyntaxError
@@ -28,8 +28,7 @@ _html_css_stylesheet = None
 def html_css_stylesheet():
     global _html_css_stylesheet
     if _html_css_stylesheet is None:
-        with open(pkg_resources.resource_filename('ebook_converter',
-                                                  'data/html.css'), 'rb') as f:
+        with open(str(files('ebook_converter').joinpath('data/html.css')), 'rb') as f:
             html_css = f.read().decode('utf-8')
         _html_css_stylesheet = parseString(html_css, validate=False)
     return _html_css_stylesheet