[codex] Support configurable database node counts

[tkilias]

Summary

• expose num_nodes in the handwritten OpenApiAccess.create_database() helper
• forward num_nodes through the OpenApiAccess.database() context helper
• add unit coverage and a live integration test for the 2-node case

Why

The generated OpenAPI client already supports numNodes, but the handwritten helper layer dropped that field. That prevented SAPIPY users from creating databases with fewer than 4 nodes through the convenience API.

Validation

• poetry run pytest test/unit/test_api_access.py in Lima VM default
• integration test added but not executed locally because it requires live SaaS credentials and provisions a real database

Fixes #147

[sonarqubecloud]

Quality Gate failed

Failed conditions
2 New Code Smells (required ≤ 0)

See analysis details on SonarQube Cloud

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[tkilias]

split up into #170 , #168 , #169 , #171