An assortment of packaging fixes

• Unpin nixpkgs here. Consider ZKAPAuthorizer a library and let the integrator pin a version. This is probably not the final word on how things should work but it helps for now.
• Downgrade the Python module typing to a version compatible with Hypothesis.
• Bump to a version of LeastAuthority/privacypass that doesn't require us to use Git submodules (which introduce an extra place for weird confusion in the packaging)
• Bump to the latest Tahoe-LAFS integration branch revision and add setuptools as an explicit runtime dependency (because it is one now)

Created by: codecov[bot]

Codecov Report

Merging #35 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #35   +/-   ##
=======================================
  Coverage   99.56%   99.56%           
=======================================
  Files          23       23           
  Lines         930      930           
=======================================
  Hits          926      926           
  Misses          4        4

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