Run RabbitMQ broker and TLS tests reliably in CI

[niemyjski]

Broker tests share owned Aspire infrastructure with real TLS verification. CI fails when required infrastructure cannot start. The main suite stays on RabbitMQ 4.2.5; a dedicated 4.3.6 broker runs the new priority upgrade cases alongside the 4.2.5 cases.

Runtime impact: test infrastructure only. Library behavior and production broker permissions are unchanged. TLS tests install a temporary certificate authority in the current user's trust store and remove it during cleanup; optional local TLS tests can skip if that installation is denied. CI starts one additional broker for priority compatibility coverage.

Validation: Release build and formatting passed. The nine new cases passed without skips on 3.13.7, 4.2.5, and 4.3.6 locally. All updated-head Linux checks passed. The push run passed 300 tests with only five expected skips from the earlier strict-quorum test on 4.2. The 19 new cases ran: nine each on 4.2.5 and 4.3.6, plus the upgrade-fixture version check.

Verification and implementation details

The version matrix compares fresh brokers. A rolling upgrade with existing queue data was not exercised.

The main, TLS, delayed-plugin, and chaos brokers remain pinned to 4.2.5. The new priority broker uses 4.3.6-management and shares the existing collection fixture and startup/cleanup lifecycle. It provides priority and routing coverage, not a complete 4.3 runtime certification.

The independent priority scenarios inherited from #106 run with version-specific assertions on both CI brokers. They cover queued ordering, omitted/zero priority, fairness, publication before subscription, and delivery already in progress. The earlier strict quorum test still skips on 4.2.5; the new cases do not skip older broker versions. None of the existing test methods change in this latest addition.

Earlier changes move fixture declarations to a shared collection. The disconnect test additionally verifies that a delivery occurred, closes the actual broker connection, and releases its blocked handler before disposal; disposal alone did not simulate an abrupt disconnect. The TCP relay forwards opaque bytes to test certificate-name failures and connection loss without weakening TLS validation. Shutdown awaits the accept loop and tunnels. Temporary certificates use asynchronous file writes and a private parent directory; broker commands target owned containers.

Merge after #106 and before #105.