Update project metadata to use SPDX license identifier

[cdce8p]

PEP 639 added support for SPDX license identifier.
Metadata diff

 ...
-License: Apache 2.0
+License-Expression: Apache-2.0
 ...
-Classifier: License :: OSI Approved :: Apache Software License
 ...

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.84%. Comparing base (cca587e) to head (2e4446f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1078   +/-   ##
=======================================
  Coverage   90.84%   90.84%           
=======================================
  Files           2        2           
  Lines         579      579           
  Branches       77       77           
=======================================
  Hits          526      526           
  Misses         32       32           
  Partials       21       21           

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[seifertm]

Thanks @cdce8p !