use uv instead of pip for payjoin-ffi/python

[nothingmuch]

This is a work in progress:

• no nix devshell support yet
• CI and README not yet updated to avoid pip
  • nonetheless uv build and uv run python -m unittest -v work
• generate_bindings.sh hackily updated to just skip over debianisms so that it runs on nixos too, this needs to be update to take the devshell into account
• it's based on Replace redis with file based mailbox storage #915, but only to remove the testcontainers dependency, see Ffi layer runtime issues #978
• add Co-authored-by with @thebrandonlucas (we pair programmed on the last 6 commits of this PR)

[coveralls]

Pull Request Test Coverage Report for Build 17884113555

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.743%

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Totals
Change from base Build 17883934451:	0.0%
Covered Lines:	8559
Relevant Lines:	10100

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💛 - Coveralls

[arminsabouri]

@thebrandonlucas will be pushing this forward

[spacebear21]

superseded by #1073