Move python test on testgres and add stress test

[CherkashinSergey]

Тесты перенесены на testgres. Добавлен стресс-тест на основе tpc-ds benchmark.

[codecov-io]

Codecov Report

Merging #12 into master will increase coverage by 11.32%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master      #12       +/-   ##
===========================================
+ Coverage   75.69%   87.01%   +11.32%     
===========================================
  Files           5        2        -3     
  Lines         469      462        -7     
===========================================
+ Hits          355      402       +47     
+ Misses        114       60       -54

Impacted Files	Coverage Δ
pg_bin/include/postgresql/server/utils/palloc.h
pg_bin/include/postgresql/server/nodes/pg_list.h
pg_bin/include/postgresql/server/storage/s_lock.h
signal_handler.c	97.4% <0%> (+5.19%)	⬆️
pg_query_state.c	84.93% <0%> (+12.98%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1cb4967...fa6ce2d. Read the comment docs.

[ololobus]

I will close it, since I have no access to the original repo, and open #16 instead.