Running backup tests only in a cluster setup

[apetenchea]

Backup tests will be skipped for single server

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Note

Low Risk
Primarily test gating plus static-analysis/dependency bumps; low runtime risk aside from potentially reduced CI coverage for backup APIs in non-cluster or older versions.

Overview
Backup integration coverage is narrowed: test_backup_management now skips on non-cluster setups and on ArangoDB versions older than 3.12.0 (using the existing db_version fixture).

Tooling/deps are tightened to align with newer typing/JWT libraries: mypy is bumped to 1.15.0 (pre-commit and dev extra), PyJWT is constrained to >=2.10.0, mypy config disables warn_unused_ignores, and JWT decode calls add # type: ignore[arg-type] to satisfy updated type checking.

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