test: Add postgres testing (#2973)

* Initial spike for database fixtures

* Simplify database initialization

* Clean up fixtures for parametrization

* Update DSL tests to use parametrized database sessions

* Clean up type annotations

* Remove needless import

* Install postgresql in github ci

* Parametrize fixture directly

* Skip postgres tests on windows and macos

* Ruff 🐶

* Only skip if flag is set

* Fix fixtures

* Update DEVELOPMENT guide

* Mark postgres tests with xfail for now

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Co-authored-by: Alexander Song <axiomofjoy@gmail.com>