Add: Add CPE function for unquoting WNF attribute values

Currently the CPE parsing model stores quoted well-formed CPE name (WNF)
attribute values. This is not ideal for using them in the application
logic. For example a version attribute will always return something like
`"1\.2\.3"` as it's value. Therefore add a new function that allows to
convert these values into their unquoted form.

pontos/cpe/_cpe.py

@@ -328,6 +328,36 @@ def unbind_value_uri(value: Optional[str]) -> Optional[str]:
     return result
 
 
+def unquote_attribute_value(value: Optional[str]) -> Optional[str]:
+    """
+    Unquote a Well-Formed CPE Name Data Model (WFN) attribute value
+    """
+    if not value or "\\" not in value:
+        # do nothing
+        return value
+
+    index = 0
+    result = ""
+    while index < len(value):
+        c = value[index]
+        if c == "\\":
+            next_c = value[index + 1]
+            if next_c in ["*", "?"]:
+                # keep escaped asterisks and question marks
+                result += f"{c}{next_c}"
+            else:
+                result += next_c
+
+            index += 2
+            continue
+        else:
+            result += c
+
+        index += 1
+
+    return result
+
+
 def split_cpe(cpe: str) -> list[str]:
     """
     Split a CPE into its parts

tests/cpe/test_cpe.py

@@ -12,6 +12,7 @@
     convert_double_backslash,
     split_cpe,
     unbind_value_from_formatted_string,
+    unquote_attribute_value,
 )
 
 
@@ -163,6 +164,26 @@ def test_unchanged(self):
         self.assertEqual(bind_value_for_formatted_string("foo\\*"), "foo\\*")
 
 
+class UnquoteAttributeValueTestCase(unittest.TestCase):
+    def test_unchanged(self):
+        self.assertIsNone(unquote_attribute_value(None))
+        self.assertEqual(unquote_attribute_value(""), "")
+        self.assertEqual(unquote_attribute_value(ANY), ANY)
+        self.assertEqual(unquote_attribute_value("?"), "?")
+        self.assertEqual(unquote_attribute_value("foo-bar"), "foo-bar")
+        self.assertEqual(unquote_attribute_value("foo_bar"), "foo_bar")
+        self.assertEqual(unquote_attribute_value("1.2.3"), "1.2.3")
+
+    def test_special(self):
+        self.assertEqual(unquote_attribute_value("foo\\?bar"), "foo\\?bar")
+        self.assertEqual(unquote_attribute_value("foo\\*bar"), "foo\\*bar")
+
+    def test_unquote(self):
+        self.assertEqual(unquote_attribute_value("foo\\\\bar"), "foo\\bar")
+        self.assertEqual(unquote_attribute_value("foo\\:bar"), "foo:bar")
+        self.assertEqual(unquote_attribute_value("1\\.2\\.3"), "1.2.3")
+
+
 class CPETestCase(unittest.TestCase):
     def test_uri_binding(self):
         cpe_string = "cpe:/o:microsoft:windows_xp:::pro"