Make it faster by getting rid of Postgres Testcontainers dependency or keeping container alive across test runs

[matthiasschaub]

• Mock Postgres connection of asyncpg
• Try out pglite wrapper https://github.com/wey-gu/py-pglite
• Implement keep_alive feature for testcontainers -> feat: reusable containers testcontainers/testcontainers-python#636