refactor(tests,lint): introduce shared cluster/eviction helpers and drop ireturn suppressions

[hyp3rd]

• Add tests/dist_cluster_helper.go with DistCluster, SetupInProcessCluster, and SetupInProcessClusterRF to replace repeated in-process cluster boilerplate in integration, remove/read-repair, stale-quorum, and heartbeat tests.
• Add heartbeat test helpers (waitForAllAlive, waitForDeadTransition, waitForNodeRemoval, nodeRemovalResult, newDistPeerNode, newDistPeerNode, assertHeartbeatLiveness) to reduce per-test function length.
• Add pkg/eviction/contract_test.go with a runEvictionContract harness that validates the IAlgorithm contract (Set/Get/Delete/Evict semantics, capacity bounds, zero-capacity no-op); replace duplicate LRU and CAWOLFU test bodies with TestLRUContract / TestCAWOLFUContract.
• Remove all //nolint:ireturn directives across production and test code; remove the golangci.yaml exclusion block that was suppressing lint rules on test files.
• Extract repeated test_value string literals in cmap_test.go into a shared testValue constant.

[Copilot]

Pull request overview

This PR refactors test infrastructure and lint configuration to reduce duplicated boilerplate across distributed-cache tests, introduces a shared eviction-algorithm contract test harness, and removes ireturn suppressions (plus the .golangci.yaml test exclusions that were masking several linters in _test.go).

Changes:

• Added shared distributed-cluster and merkle-node test helpers and updated multiple dist/merkle/heartbeat tests to use them.
• Introduced an eviction IAlgorithm contract test harness and replaced duplicated LRU/CAWOLFU test bodies with contract coverage.
• Removed //nolint:ireturn directives broadly and removed .golangci.yaml test-file exclusion rules; extracted repeated test constants to satisfy goconst.

Reviewed changes

Copilot reviewed 42 out of 43 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/merkle_sync_test.go	Uses a shared merkle node helper to cut setup boilerplate.
tests/merkle_node_helper.go	Adds newMerkleNode helper for merkle-sync tests.
tests/merkle_delete_tombstone_test.go	Refactors merkle tombstone test to use newMerkleNode.
tests/management_http_test.go	Extracts management listener wait loop into helper.
tests/key_owner_helper.go	Drops ireturn suppression from FindOwnerKey.
tests/integration/dist_rebalance_test.go	Extracts shared options + key population helpers for rebalance tests.
tests/integration/dist_phase1_test.go	Extracts node creation + replication wait helpers; cleans up value matching logic.
tests/hypercache_set_test.go	Extracts shared test key/value constants to satisfy goconst.
tests/hypercache_mgmt_dist_test.go	Adds helper to assert mgmt endpoint JSON shape with clearer failures.
tests/hypercache_http_merkle_test.go	Extracts HTTP merkle node creation + endpoint readiness polling helpers.
tests/hypercache_get_test.go	Refactors Get tests into a shared case runner + typed case struct.
tests/hypercache_get_or_set_test.go	Refactors GetOrSet tests into a shared case runner + typed case struct.
tests/hypercache_get_multiple_test.go	Reuses shared key constants for multi-get tests.
tests/hypercache_distmemory_write_quorum_test.go	Uses shared in-process cluster helper; simplifies quorum failure setup.
tests/hypercache_distmemory_versioning_test.go	Uses shared in-process cluster helper; extracts deterministic owner-key search.
tests/hypercache_distmemory_tiebreak_test.go	Uses shared in-process cluster helper; reuses deterministic owner-key search.
tests/hypercache_distmemory_stale_quorum_test.go	Uses shared in-process cluster helper; extracts requester selection helper.
tests/hypercache_distmemory_remove_readrepair_test.go	Replaces bespoke two-node fixture with shared in-process cluster helper.
tests/hypercache_distmemory_integration_test.go	Uses shared in-process cluster helper for forwarding/replication integration test.
tests/hypercache_distmemory_hinted_handoff_test.go	Extracts hinted-handoff helpers (key selection, metrics assertions, node creation).
tests/hypercache_distmemory_heartbeat_test.go	Extracts heartbeat liveness polling/assertion helpers and uses shared peer creation helper.
tests/hypercache_distmemory_heartbeat_sampling_test.go	Adds reusable heartbeat peer creation + dead-transition polling helper.
tests/hypercache_distmemory_failure_recovery_test.go	Refactors failure/recovery test using shared cluster + extracted hint/transition helpers.
tests/dist_cluster_helper.go	Adds shared DistCluster fixture + SetupInProcessCluster* constructors.
pkg/eviction/lru_test.go	Removes duplicated contract-style LRU tests (now covered by contract harness).
pkg/eviction/contract_test.go	Adds shared IAlgorithm contract test harness and runs it for LRU + CAWOLFU.
pkg/eviction/clock.go	Removes ireturn suppressions from helpers.
pkg/eviction/cawolfu_test.go	Removes duplicated contract-style CAWOLFU tests (now covered by contract harness).
pkg/cache/v2/cmap_test.go	Extracts repeated "test_value" into a constant.
pkg/backend/inmemory.go	Removes ireturn suppression from Touch.
pkg/backend/dist_transport.go	Removes ireturn suppressions from in-process transport methods.
pkg/backend/dist_memory_test_helpers.go	Removes ireturn suppressions from dist-memory test helpers.
pkg/backend/dist_memory.go	Removes ireturn suppressions across options/helpers and public methods.
pkg/backend/dist_latency.go	Removes ireturn suppressions from latency collector helpers.
pkg/backend/dist_http_transport.go	Removes ireturn suppressions from HTTP transport methods/helpers.
pkg/backend/dist_http_server.go	Removes ireturn suppressions from HTTP server methods.
management_http.go	Removes ireturn suppressions from management HTTP server helpers.
internal/transport/transport.go	Removes ireturn suppression from RPCError.Error().
internal/dist/config.go	Removes ireturn suppression from Defaults().
internal/cluster/membership.go	Removes ireturn suppressions from membership methods.
hypercache.go	Removes ireturn suppressions from dist introspection helpers.
cspell.config.yaml	Adds ignore patterns + dictionary words for new terminology.
.golangci.yaml	Removes test-file linter exclusion block so tests run under full lint rules.

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