Enable the Ruff `SIM` checks family

[fizyk]

Summary

Enable the Ruff SIM (flake8-simplify) checks family in the project lint configuration.

Rationale

The current review identified nested context managers that Ruff rule SIM117 can simplify. Enabling the complete SIM checks family will detect similar maintainability issues consistently during local development and continuous integration.

Affected areas

• Ruff configuration
• Existing Python source and test files that fail newly enabled SIM rules

Required changes

1. Update the Ruff configuration to enable the SIM checks family.
2. Run Ruff against the repository.
3. Apply minimal code changes for any newly reported valid SIM findings.
4. Document any intentional exclusions in the Ruff configuration, if exclusions are necessary.

Acceptance criteria

• Ruff selects the SIM checks family.
• The repository passes Ruff with the enabled checks.
• Any exclusions have a documented reason.

Backlinks

• Requested by @fizyk.
• Pull request: Cleaner error message when the server is not installed - closes #1031 pytest-postgresql#1396
• Review comment: Cleaner error message when the server is not installed - closes #1031 pytest-postgresql#1396 (comment)

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Copied from dbfixtures/pytest-postgresql#1404