Switch CI to CircleCI, drop Windows testing

[smoia]

Closes #

Proposed Changes

• Leaving Cirrus CI in favour of Circle CI due to the intensive use of credits
• Also dropping testing for Windows, at least for the moment, as they take too many credits to be a sustainable support.

Change Type

• bugfix (+0.0.1)
• minor (+0.1.0)
• major (+1.0.0)
• refactoring (no version update)
• test (no version update)
• infrastructure (no version update)
• documentation (no version update)
• other

Checklist before review

• I added everything I wanted to add to this PR.
• [Code or tests only] I wrote/updated the necessary docstrings.
• [Code or tests only] I ran and passed tests locally.
• [Documentation only] I built the docs locally.
• My contribution is harmonious with the rest of the code: I'm not introducing repetitions.
• My code respects the adopted style, especially linting conventions.
• The title of this PR is explanatory on its own, enough to be understood as part of a changelog.
• I added or indicated the right labels.

• I added information regarding the timeline of completion for this PR.

• Please, comment on my PR while it's a draft and give me feedback on the development!

[codecov]

Codecov Report

Merging #430 (f39f937) into master (68f3f42) will not change coverage.
The diff coverage is n/a.

❗ Current head f39f937 differs from pull request most recent head e377344. Consider uploading reports for the commit e377344 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #430   +/-   ##
=======================================
  Coverage   94.42%   94.42%           
=======================================
  Files           8        8           
  Lines         879      879           
=======================================
  Hits          830      830           
  Misses         49       49