Fix thread safety issue in patron_activity (PP-1155)

[jonathangreen]

Description

This fixes a thread safety issue, where SQLAlchemy objects that are part of one thread's session are used in another thread. Leading to unpredictable behavior and deadlocks among the threads when under load. This was causing issues in the California CM instance when it was under increased load due to Aspen integration.

Motivation and Context

Resolve issues where threads and workers deadlock with each other, trying to update the patron information.

How Has This Been Tested?

• Tested locally with CA DB and UWSGI
• I wasn't able to make it deadlock, the way I see in production but I did see worker threads flushing changes from the main thread's Session.
• This seems to indicate my hypothesis of session mixing is at least a possible cause here.

Checklist

• I have updated the documentation accordingly.
• All new and existing tests passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.31%. Comparing base (8e97653) to head (1f3fc57).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1793   +/-   ##
=======================================
  Coverage   90.30%   90.31%           
=======================================
  Files         259      259           
  Lines       28659    28659           
  Branches     6514     6514           
=======================================
+ Hits        25881    25883    +2     
+ Misses       1840     1839    -1     
+ Partials      938      937    -1     

Flag	Coverage Δ
Api	75.57% <ø> (+<0.01%)	⬆️
Core	59.79% <ø> (ø)
migration	24.08% <ø> (+0.02%)	⬆️

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[tdilauro]

🧵🚨 Looks great!

I made a couple minor edits to the main PR description.