Configure Cirrus CI

[fkorotkov]

Cirrus CI allows to use more than 2 CPUs which speeds up tests drastically:

Cirrus CI also provides more flexibility by using containers and very fast caching storage.

In case you'll decide to merge, an admin of Twitter organization must install Cirrus CI App from GitHub Marketplace: https://github.com/marketplace/cirrus-ci

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (develop@d5322b3). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             develop     #767   +/-   ##
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  Coverage           ?   71.48%           
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  Files              ?      151           
  Lines              ?     3616           
  Branches           ?      208           
==========================================
  Hits               ?     2585           
  Misses             ?     1031           
  Partials           ?        0

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[johnynek]

This is interesting! Thanks for sending the PR.

We need to ask Remy or maybe Timur can help us find the right folks.

[fkorotkov]

Sure thing! @ttim was complaining about unstable CI so I took a look 😅