OPS-REF-002D: split PostgreSQL execution helpers

[ktalpay]

Motivation

• Consolidate low-level database execution, fetch and transaction calls into a single reusable module to reduce duplication while preserving existing repository orchestration and behavior.

Description

• Added src/carbonfactor_parser/persistence/postgresql_execution.py with execute, fetchone, commit, and rollback that retain the original getattr-based calling semantics and parameter handling.
• Updated src/carbonfactor_parser/persistence/postgresql_source_family_repository.py to import and use the new helpers in place of the internal _execute/_fetchone/_commit/_rollback functions and removed those internal helpers.
• Added focused tests in tests/test_postgresql_execution.py that verify execute calls with and without parameters, fetchone calls, and commit/rollback behavior when the methods are present or absent.

Testing

• Ran python -m pytest tests/test_postgresql_source_family_repository.py which completed with 21 passed, 1 skipped.
• Ran the full test-suite with python -m pytest which completed with 2169 passed, 8 skipped.
• Ran lint checks with python -m ruff check on the modified files and the checks passed.

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Codex Task