Fix DAL session management to support connection pooling

[DanPaseltiner]

PULL REQUEST

Summary

This PR introduces changes to how the MPI client manages SQLAlchemy sessions and schema initialization in order to support connection pooling.

Related Issue

Fixes #

Additional Information

Anything else the review team should know?

Checklist

• If this code affects the other scrum team, have they been notified? (In Slack, as reviewers, etc.)

[m-goggins]

Looks good! Just deleted one final print statement

[codecov]

Codecov Report

Merging #911 (c03e709) into main (c4b5712) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #911      +/-   ##
==========================================
+ Coverage   96.38%   96.48%   +0.10%     
==========================================
  Files          48       48              
  Lines        2820     2820              
==========================================
+ Hits         2718     2721       +3     
+ Misses        102       99       -3     

Flag	Coverage Δ
unit-tests	96.48% <100.00%> (+0.10%)	⬆️

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Files	Coverage Δ
phdi/linkage/dal.py	100.00% <100.00%> (+2.91%)	⬆️
phdi/linkage/mpi.py	96.15% <100.00%> (+0.04%)	⬆️