Improve logging

[duncanmmacleod]

This PR improves the debug logging for Sessions, mainly by using nullcontext to ensure that existing connections aren't closed twice when nested.

[codecov]

Codecov Report

Merging #102 (f8ac000) into main (1a6d4eb) will increase coverage by 0.72%.
The diff coverage is 86.48%.

❗ Current head f8ac000 differs from pull request most recent head de6592f. Consider uploading reports for the commit de6592f to get more accurate results

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
+ Coverage   88.09%   88.81%   +0.72%     
==========================================
  Files          30       31       +1     
  Lines        1050     1073      +23     
==========================================
+ Hits          925      953      +28     
+ Misses        125      120       -5     

Flag	Coverage Δ
Linux	88.81% <86.48%> (+0.72%)	⬆️
Windows	88.03% <86.48%> (+0.83%)	⬆️
macOS	88.81% <86.48%> (+0.72%)	⬆️
python3.10	87.88% <72.97%> (+0.26%)	⬆️
python3.6	88.39% <86.48%> (+0.75%)	⬆️
python3.7	87.91% <72.97%> (+0.27%)	⬆️
python3.8	88.16% <72.97%> (+0.25%)	⬆️
python3.9	88.16% <72.97%> (+0.25%)	⬆️

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Impacted Files	Coverage Δ
ciecplib/__init__.py	100.00% <ø> (ø)
ciecplib/tool/ecp_get_cert.py	57.40% <0.00%> (+2.05%)	⬆️
ciecplib/requests.py	89.18% <77.77%> (+15.27%)	⬆️
ciecplib/kerberos.py	100.00% <100.00%> (ø)
ciecplib/logging.py	100.00% <100.00%> (ø)
ciecplib/sessions.py	92.59% <100.00%> (+4.13%)	⬆️
ciecplib/tests/test_requests.py	100.00% <100.00%> (ø)
ciecplib/tests/test_kerberos.py	100.00% <0.00%> (ø)
... and 1 more

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[duncanmmacleod]

The reduction in coverage will be addressed by #106.