Fix: https://github.com/grpc/grpc/issues/34690
Also added generated proto files to example folder so we can run example
directly.
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- Switched from yapf to black
- Reconfigure isort for black
- Resolve black/pylint idiosyncrasies
Note: I used `--experimental-string-processing` because black was
producing "implicit string concatenation", similar to what described
here: https://github.com/psf/black/issues/1837. While currently this
feature is experimental, it will be enabled by default:
https://github.com/psf/black/issues/2188. After running black with the
new string processing so that the generated code merges these `"hello" "
world"` strings concatenations, then I removed
`--experimental-string-processing` for stability, and regenerated the
code again.
To the reviewer: don't even try to open "Files Changed" tab 😄 It's
better to review commit-by-commit, and ignore `run black and isort`.
