Make the Requirements API asynchronous

[bartfeenstra]

This fixes #1363

[github-actions]

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[github-actions]

Uploaded Betty for commit 70bca90. You can download it, test it, and post your feedback in a comment to this pull request 💕

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[github-actions]

Uploaded Betty for commit 0646536. You can download it, test it, and post your feedback in a comment to this pull request 💕

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• Betty Desktop for Windows 🪟

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[codecov]

Codecov Report

Attention: Patch coverage is 98.18182% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.82%. Comparing base (817eb2f) to head (05e8283).
Report is 325 commits behind head on 0.4.x.

Files with missing lines	Patch %	Lines
betty/project/__init__.py	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            0.4.x    #1590   +/-   ##
=======================================
  Coverage   95.82%   95.82%           
=======================================
  Files         183      183           
  Lines       16524    16524           
  Branches     3310     3310           
=======================================
  Hits        15834    15834           
  Misses        477      477           
  Partials      213      213           

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