fix: use tuple comparison for python-multipart version check

String comparison is lexicographic, so "0.0.100" > "0.0.12" evaluates to
False ("1" < "9" by char code). A valid python-multipart==0.0.100+
installation was incorrectly rejected as too old, raising multipart_not_installed_error
on any Form() or File() endpoint.

Parse the version into an integer tuple before comparing so numeric ordering
is used instead.

fastapi/dependencies/utils.py

@@ -96,7 +96,7 @@ def ensure_multipart_is_installed() -> None:
         from python_multipart import __version__
 
         # Import an attribute that can be mocked/deleted in testing
-        assert __version__ > "0.0.12"
+        assert tuple(int(x) for x in __version__.split(".")[:3]) > (0, 0, 12)
     except (ImportError, AssertionError):
         try:
             # __version__ is available in both multiparts, and can be mocked