Add typing_extensions as core dependency and add install from conda GHA test

[valeriupredoi]

Description

W have to add typing_extensions as a core dependency since otherwise the package fails to import correctly, I have just rebuilt the conda package with that in mind at conda-forge/pyfive-feedstock#25 and PyPI package will be updated from the next release onwards, after this gets merged. I also added a conda install GHA test.

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• ☝ Create an issue to discuss what you are going to do

Checklist

• This pull request has a descriptive title and labels
• This pull request has a minimal description (most was discussed in the issue, but a two-liner description is still desirable)
• Unit tests have been added (if codecov test fails)
• Any changed dependencies have been added or removed correctly (if need be)
• If you are working on the documentation, please ensure the current build passes
• All tests pass

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.62%. Comparing base (026e388) to head (11aa5eb).
⚠️ Report is 73 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #202   +/-   ##
=======================================
  Coverage   77.62%   77.62%           
=======================================
  Files          15       15           
  Lines        3128     3128           
  Branches      499      499           
=======================================
  Hits         2428     2428           
  Misses        573      573           
  Partials      127      127           

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