Split Specifier regex into operator and version parts

Tokenizer uses _version_regex_str to detect 'VERSION' token.

Author: hrnciar

packaging/specifiers.py

@@ -316,8 +316,10 @@ def wrapped(self: "Specifier", prospective: ParsedVersion, spec: str) -> bool:
 
 class Specifier(_IndividualSpecifier):
 
-    _regex_str = r"""
+    _operator_regex_str = r"""
         (?P<operator>(~=|==|!=|<=|>=|<|>|===))
+        """
+    _version_regex_str = r"""
         (?P<version>
             (?:
                 # The identity operators allow for an escape hatch that will
@@ -409,7 +411,10 @@ class Specifier(_IndividualSpecifier):
         )
         """
 
-    _regex = re.compile(r"^\s*" + _regex_str + r"\s*$", re.VERBOSE | re.IGNORECASE)
+    _regex = re.compile(
+        r"^\s*" + _operator_regex_str + _version_regex_str + r"\s*$",
+        re.VERBOSE | re.IGNORECASE,
+    )
 
     _operators = {
         "~=": "compatible",