Fix typing of Parser's unbound methods

All credit due to "Finite State Machine" on the typing gitter, they're
the one who had the idea of trying to type `self` in case that would
make mypy happy. Which it absolutely does.

This does make that use pattern easier to recommend, as it's fully
typed as well.

src/ua_parser/__init__.py

@@ -93,25 +93,25 @@ def __call__(self, ua: str, domains: Domain, /) -> PartialParseResult:
         """
         return self.resolver(ua, domains)
 
-    def parse(self, ua: str) -> ParseResult:
+    def parse(self: Resolver, ua: str) -> ParseResult:
         """Convenience method for parsing all domains, and falling back to
         default values for all failures.
         """
         return self(ua, Domain.ALL).complete()
 
-    def parse_user_agent(self, ua: str) -> Optional[UserAgent]:
+    def parse_user_agent(self: Resolver, ua: str) -> Optional[UserAgent]:
         """Convenience method for parsing the :class:`UserAgent` domain,
         falling back to the default value in case of failure.
         """
         return self(ua, Domain.USER_AGENT).user_agent
 
-    def parse_os(self, ua: str) -> Optional[OS]:
+    def parse_os(self: Resolver, ua: str) -> Optional[OS]:
         """Convenience method for parsing the :class:`OS` domain, falling back
         to the default value in case of failure.
         """
         return self(ua, Domain.OS).os
 
-    def parse_device(self, ua: str) -> Optional[Device]:
+    def parse_device(self: Resolver, ua: str) -> Optional[Device]:
         """Convenience method for parsing the :class:`Device` domain, falling
         back to the default value in case of failure.
         """

tests/test_convenience_parser.py

@@ -1,13 +1,19 @@
-from ua_parser import Parser, ParseResult, PartialParseResult
+from ua_parser import Domain, Parser, ParseResult, PartialParseResult
+
+
+def resolver(s: str, d: Domain) -> PartialParseResult:
+    return PartialParseResult(d, None, None, None, s)
 
 
 def test_parser_utility() -> None:
     """Tests that ``Parser``'s methods to behave as procedural
     helpers, for users who may not wish to instantiate a parser or
     something.
 
-    Sadly the typing doesn't really play nicely with that.
-
     """
-    r = Parser.parse(lambda s, d: PartialParseResult(d, None, None, None, s), "a")  # type: ignore
+
+    r = Parser.parse(resolver, "a")
     assert r == ParseResult(None, None, None, "a")
+
+    os = Parser.parse_os(resolver, "a")
+    assert os is None