Revert normalize performance changes (gh-143658) in __init__.py

Reverts the importlib_metadata/__init__.py normalize() changes introduced
by the merge 8c5d91b (str.translate/replace optimizations from
3e7f3ac and 001db0d), restoring the original re.sub-based
implementation.

Closes #540

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: jaraco

importlib_metadata/__init__.py

@@ -962,15 +962,8 @@ def __init__(self, name: str | None):
     def normalize(name):
         """
         PEP 503 normalization plus dashes as underscores.
-
-        Specifically avoids ``re.sub`` as prescribed for performance
-        benefits (see python/cpython#143658).
         """
-        value = name.lower().replace("-", "_").replace(".", "_")
-        # Condense repeats
-        while "__" in value:
-            value = value.replace("__", "_")
-        return value
+        return re.sub(r"[-_.]+", "-", name).lower().replace('-', '_')
 
     @staticmethod
     def legacy_normalize(name):