Add tests for durable receiver listener null

[Joelgullander]

Summary

• Add a unit test to reproduce the latched durable receiver NRE when Envelope.Listener is null.
• Add a slow integration test that loads an envelope from the durable inbox (Postgres) and reproduces the NRE via the redelivery path.
• Wire Wolverine.Postgresql into SlowTests for the integration repro.

Test plan

• dotnet test src/Testing/CoreTests/CoreTests.csproj --filter durable_receiver_latched_without_listener
• dotnet test src/Testing/SlowTests/SlowTests.csproj --filter durable_receiver_redelivery_from_inbox

Related to #2258