Copy globals dict during iteration

[adamnovak]

This will fix #325 by preventing modifications to globals() from other threads from producing a RuntimeError: dictionary changed size during iteration while we look for keycodes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.33%. Comparing base (dc1e596) to head (73086bd).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #326   +/-   ##
=======================================
  Coverage   98.33%   98.33%           
=======================================
  Files          11       11           
  Lines        2468     2468           
  Branches      429      429           
=======================================
  Hits         2427     2427           
  Misses         31       31           
  Partials       10       10           

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