update-python-libraries: support pyproject and flit formats

Generally, this is determined by the fetcher. The
notable exception would be the "wheel" format.

pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py

···
 
 FORMATS = {
     'setuptools'        :   DEFAULT_SETUPTOOLS_EXTENSION,
-    'wheel'             :   'whl'
+    'wheel'             :   'whl',
+    'pyproject'         :   'tar.gz',
+    'flit'              :   'tar.gz'
 }
 
 def _determine_fetcher(text):
···
         if extension is None:
             if src_format is None:
                 src_format = 'setuptools'
-            elif src_format == 'flit':
-                raise ValueError("Don't know how to update a Flit package.")
             elif src_format == 'other':
                 raise ValueError("Don't know how to update a format='other' package.")
-            elif src_format == 'pyproject':
-                raise ValueError("Don't know how to update a pyproject package.")
             extension = FORMATS[src_format]
 
     elif fetcher == 'fetchurl':