Add typing_extensions to pyproject.toml dependencies

[Jasha10]

Closes #412.

[CLAassistant]

All committers have signed the CLA.

[tony]

Thank you for the PR (And for the issue at #412 as well), @Jasha10!

As for if we go this way: Maybe. There is one more thing I want to try

I am going to try an approach that uses type guards to (attempt) to stave off the extra dependency. If that doesn't pan out, I will merge the approach

[codecov]

Codecov Report

Merging #413 (e25b00f) into master (18a73e4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #413   +/-   ##
=======================================
  Coverage   84.00%   84.00%           
=======================================
  Files          17       17           
  Lines         938      938           
  Branches      168      168           
=======================================
  Hits          788      788           
  Misses        100      100           
  Partials       50       50           

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[Jasha10]

Closing -- this PR is obviated now that #414 is merged.

[tony]

Should maintaining the pattern in #414 be too much to maintain dependably we can re-open this in the future.