Fix issue where Python sources can deadlock when the subscriber is unsubscribed

[dagardner-nv]

Description

• Ensures that Python source nodes shutdown when their subscriber is unsubscribed
• Advance the underlying Python iterator inside of it's own thread pushing values to a queue.
• Execute generator in a thread created by the Python interpreter, this allows us to stop the thread on shutdown via the CPython API by raising an exception in the thread.
• Remove unused json usage in python/mrc/_pymrc/src/utilities/acquire_gil.cpp
• Update conftest.py to set the loglevel to DEBUG if the GLOG_v environment variable is defined.

Closes nv-morpheus/Morpheus#1838

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[codecov]

Codecov Report

Attention: Patch coverage is 89.79592% with 10 lines in your changes missing coverage. Please review.

Project coverage is 74.16%. Comparing base (ca8a73f) to head (8b4c59c).

Files with missing lines	Patch %	Lines
python/mrc/_pymrc/src/segment.cpp	89.69%	10 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-24.10     #495      +/-   ##
================================================
+ Coverage         74.06%   74.16%   +0.10%     
================================================
  Files               403      403              
  Lines             14403    14475      +72     
  Branches           1132     1143      +11     
================================================
+ Hits              10667    10736      +69     
- Misses             3736     3739       +3     

Flag	Coverage Δ
cpp	70.46% <1.02%> (-0.35%)	⬇️
py	42.78% <91.66%> (+0.95%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
python/mrc/_pymrc/include/pymrc/segment.hpp	62.50% <ø> (ø)
python/mrc/_pymrc/src/utilities/acquire_gil.cpp	57.14% <ø> (ø)
python/mrc/core/segment.cpp	95.78% <100.00%> (+0.04%)	⬆️
python/mrc/_pymrc/src/segment.cpp	84.27% <89.69%> (+2.58%)	⬆️

... and 8 files with indirect coverage changes

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