refactor: make ClusterType a Protocol

[mkoura]

The base class carried no shared behavior, only stubs raising NotImplementedError. As a structural Protocol:

• The LOCAL/TESTNET constants move to a new ClusterKind StrEnum and the type attribute is typed by it, eliminating the "unknown" placeholder state.
• Consumers use new is_local/is_testnet properties (concrete protocol defaults) instead of comparing .type to constants.
• NODES becomes a frozenset, as it is shared class state exposed on a process-wide cached singleton.
• test_addr_records moves to a module-level TEST_ADDR_RECORDS constant, as it was never used outside the implementations.
• LocalCluster implements testnet_type explicitly instead of inheriting the base default.
• Type checkers now treat all protocol members as abstract for the implementations, so a cluster type that forgets to define a method or the cluster_scripts attribute is a type error instead of a runtime surprise.

[Copilot]

Pull request overview

This PR refactors cluster-type handling by replacing the previous stub-only ClusterType base class with a structural Protocol, introducing a ClusterKind StrEnum, and updating consumers to use protocol-provided is_local/is_testnet checks. This better aligns runtime behavior with typing expectations and removes the prior “unknown” placeholder state.

Changes:

• Introduce ClusterKind and convert ClusterType to a Protocol with default helpers (is_local, is_testnet) and abstract members.
• Convert shared cluster node lists to immutable frozenset and move address-record data to a module constant (TEST_ADDR_RECORDS).
• Update call sites across utils/tests to use is_local/is_testnet instead of .type == ... comparisons.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
cardano_node_tests/utils/logfiles.py	Switch testnet detection to is_testnet.
cardano_node_tests/utils/governance_setup.py	Switch testnet detection to is_testnet for default-governance guard.
cardano_node_tests/utils/cluster_nodes.py	Introduce ClusterKind, ClusterType protocol, immutable NODES, and TEST_ADDR_RECORDS; update implementations.
cardano_node_tests/tests/tests_conway/test_guardrails.py	Use is_local for local-only skip logic.
cardano_node_tests/tests/tests_conway/test_drep.py	Use is_local for local-only skips and conditional behavior.
cardano_node_tests/tests/test_mir_certs.py	Update shortcut skip condition to use is_local.
cardano_node_tests/tests/test_cli.py	Use is_local for local-only error dumping.
cardano_node_tests/tests/plutus_common.py	Use is_testnet for testnet early-return.
cardano_node_tests/tests/delegation.py	Use is_testnet to select testnet behavior path.
cardano_node_tests/tests/conftest.py	Use is_testnet / is_local for cleanup and respin gating.
cardano_node_tests/tests/common.py	Update skip markers and local/testnet branching; adjust set type after NODES becomes frozenset.
cardano_node_tests/cluster_management/cluster_getter.py	Use is_local for timeout selection.

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