pyo3 (and part of the ecosystem): upgrade to 0.21.1

This drops the in-tree (but unreleased) version from 0.22.0 to 0.21.1, since the rest of the pyo3 ecosystem doesn't appear to be there yet.

pep508_rs is experiencing an package test failure, but I'm not yet quite skilled enough to understand what is going on there.

pep508 and pep440 required new packages, packaged here.

pythonize, pyo3-log, and pyproject-toml also get upgrades

I don't think this is needed or has any effect?

This author seems to be very conservative in their stated requirements. I expect that this will make future updates more likely to succeed, assuming that serde continues to follow semantic versioning. But, I can remove it if you'd like.

it's always nice to give the order of things for bigger MRs, else a reviewer has to find out on their own which is extra work ;)

FWIW, I tested using the following order:

pyo3-build-config
pyo3-ffi
pyo3-macros-backend
pyo3-macros
pyo3
pyo3-log
unscanny
pep440_rs
pubgrub
pep508_rs
pythonize
pyproject-toml

noted a few small things, in addition to those:

• pyo3 is patched to use memoffset 0.6, unstable has 0.8 now -> needs a small fix
• pyo3 has a few patches which are not referenced in the series file (?)
• pyo3 triggers a lintian check that might be overridden or handled (executable-not-elf-or-script, probably those .rs files shouldn't be executable..)
• the failing pep508_rs test case for the tracing feature seems to be either a lacking feature guard (for the pyo3 feature in addition to the tracing feature), or a missing dep for the tracing feature (to enable tracing/log, like the pyo3 feature does). when in doubt, asking upstream seems fair, and choosing one of the two for now or marking that particular test invocation as broken all seem like valid options to proceed

1. This was fixed by a rebase.
2. I've removed the one still remaining.
3. I've modified debian/rules to chmod -x those files after dh_install. Is that acceptable?
4. I've added a pyo3 feature guard for now.

requested review from @fg

added 184 commits

• 9aec4b63...dd924a66 - 175 commits from branch rust-team:master
• 921972fd - pyo3: import 0.21.2
• 1f38376e - Cleanup pyo3 patches directory
• ccd5448c - pyo3-log: upgrade to 0.10.0
• f8b817ba - pythonize: upgrade to 0.21.1
• 957d6410 - unscanny: package 0.1
• ff98753f - pep440_rs: upgade to 0.6.0
• 501b6f50 - pubgrub: import 0.2.1
• c465abfa - pep508_rs: upgrade to 0.6.0
• 9b9ef6fd - pyproject-toml: upgrade to 0.11.0

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