Use pypi PURLs instead of plain pypi names

This allows us to include a version and we already use PURL
for other things, so might as well remove the pypi special case.

Normalize the names, since that is required for PURLs.

python-fastbencode/PKGBUILD

@@ -7,7 +7,7 @@ pkgdesc='Implementation of bencode with optional fast C extensions'
 arch=('i686' 'x86_64')
 url='https://github.com/breezy-team/fastbencode'
 msys2_references=(
-  "pypi: fastbencode"
+  "purl: pkg:pypi/fastbencode"
 )
 license=(spdx:GPL-2.0-or-later)
 depends=(python)