Use palloc() and pfree() in pgsm_ExecutorRun()

[jeltz]

There is no reason not to use PostgreSQL's allocator here. It is a bit doubtful that we should call pfree() in the error path but changing that would complicate the code a bit.

PG-0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.46%. Comparing base (81ca012) to head (ae4b530).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #825   +/-   ##
=======================================
  Coverage   88.46%   88.46%           
=======================================
  Files           3        3           
  Lines        1318     1318           
  Branches      187      187           
=======================================
  Hits         1166     1166           
  Misses         77       77           
  Partials       75       75           

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