replace usages of pkg_resources with importlib.metadata

[zacharyburnett]

Changes

attempting to fix issues in readthedocs build:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/weldx/checkouts/940/doc/src/conf.py", line 65, in <module>
    import weldx
  File "/home/docs/checkouts/readthedocs.org/user_builds/weldx/conda/940/lib/python3.10/site-packages/weldx/__init__.py", line 144, in <module>
    import weldx.config
  File "/home/docs/checkouts/readthedocs.org/user_builds/weldx/conda/940/lib/python3.10/site-packages/weldx/config.py", line 8, in <module>
    import pkg_resources
  File "/home/docs/checkouts/readthedocs.org/user_builds/weldx/conda/940/lib/python3.10/site-packages/pkg_resources/__init__.py", line 105, in <module>
    from _typeshed import BytesPath, StrPath, StrOrBytesPath
ModuleNotFoundError: No module named '_typeshed'

https://readthedocs.org/projects/weldx/builds/25043814/

Related Issues

Checks

• updated CHANGELOG.md
• updated tests/
• updated doc/
• update example/tutorial notebooks
• update manifest file

[github-actions]

Test Results

2 188 tests  ±0   2 187 ✅ ±0   1m 56s ⏱️ -1s
    1 suites ±0       1 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit c7585e6. ± Comparison against base commit b5e2131.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.42%. Comparing base (5ad2929) to head (c7585e6).
Report is 23 commits behind head on master.

Files with missing lines	Patch %	Lines
weldx/config.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #941      +/-   ##
==========================================
- Coverage   96.48%   96.42%   -0.06%     
==========================================
  Files          95       95              
  Lines        6293     6301       +8     
==========================================
+ Hits         6072     6076       +4     
- Misses        221      225       +4     

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[CagtayFabry]

Thank you for starting this @zacharyburnett ! This was bothering me for a long time.
I included some changes to simplify version specific parts of the code as well, I hope you don't mind me using this PR.