vdirsyncer: Convert to a python module (#87865)

* vdirsyncer: standardize derivation

Use toPythonApplication and use callPackage from python-packages.nix.
Make vdirsyncerStable somewhat functional again, but mark it as broken
for Python 3.6 or higher.

* vdirsyncer: use buildPythonPackage as it's a package now

* vdirsyncer: move to python-modules/

* vdirsyncer: Move disabled logic into expression