fix: allow cluster profiles without database engine

[fallintoplace]

Summary

• normalize an omitted database_engine before evaluating cluster support
• add parameterized coverage for empty, standard, and replicated database engines

Details

database_engine is optional in profile credentials. When a cluster was configured without it, the adapter passed None to the cluster helper, which then called .lower() and stopped compilation.

Testing

• pytest tests/unit -q
• Ruff format, lint, and mypy checks for changed files
• YAML lint

[koletzilla]

Hi @fallintoplace thanks for your PRs!

Can you please:

• Add a changelog to each of them similar as the rest of the rest of changelogs entries. As these are small fixes, please keep each changelog small.
• Rebase your branch on top of latest main

[koletzilla]

Thanks for the PR!