test: stabilize integration tests against dev-server slowness

[jmaeagle99]

What was changed

• Consolidate integration test CLI version
• Consolidate client creation
• Reorder config callbacks to be applied last
• Use database file for payload limits tests

Why?

Various connection issues have appeared lately in tests. Some indications show that:

• The client GetSystemInfoTimeout was too short (fixed by consolidating client creation)
• Payload limits tests were not using the correct namespace (fixed by reordering config callbacks)
• Resetting client and worker in payload limits tests is causing contention in database connections (fixed by using database file so connection pooling is enabled, just like main integration test suite).