Reverts the StaticPool fix (68bc068) as it is no longer needed on
develop-hamza-2. Restores the original SingletonThreadPool default
for sqlite:///:memory: engine creation.
The default SingletonThreadPool for sqlite:///:memory: can
non-deterministically lose flushed data when multiple sessions are
created without closing (as in the bulk-register table step).
Under CI with coverage --parallel-mode and behave-parallel --processes 32,
this caused list_all() to return 2 skills instead of 3.
StaticPool guarantees all sessions share the exact same DBAPI connection,
which is the SQLAlchemy-recommended pattern for :memory: test databases.
khyari hamza
CoreRasurae
