[Event Hubs] Add live tests for owner level (epoch) arbitration

## Summary

`OpenReceiverOptions` supports `owner_level`, but no live test sets it directly. The only coverage is indirect: `second_processor_displaces_first_with_consumer_disconnected` in `eventhubs_processor.rs` exercises one displacement path through the event processor. .NET has about 10 tests each in `EventHubConsumerClientLiveTests` and `PartitionReceiverLiveTests`.

## Motivation

Owner level is how the service arbitrates between competing readers on one partition. The broker decides who wins and who gets disconnected, so only a live test can prove the behavior. This logic also underpins the event processor, so a regression here breaks partition ownership. Part of #4886.

## Proposal

- [ ] An exclusive receiver displaces an active non exclusive receiver on the same partition (.NET `ExclusiveConsumerSupersedesNonExclusiveActiveReader`).
- [ ] A receiver with a higher owner level displaces a receiver with a lower owner level (.NET `ConsumerWithHigherOwnerLevelSupersedesActiveReader`).
- [ ] A receiver with a lower owner level cannot open while a higher level receiver is active (.NET `ConsumerCannotReadWithLowerOwnerLevelThanActiveReader`).
- [ ] Displacement does not cross partitions and does not cross consumer groups (.NET `ExclusiveConsumerDoesNotSupersedeNonExclusiveActiveReaderOnAnotherPartition` and the consumer group twin).

The test namespace is shared across the whole suite. Use distinct consumer groups or distinct partitions in these tests, so that a displacement in one test does not disturb another test.

## Validation

Deploy the test resources with `eng/common/TestResources/New-TestResources.ps1 -ServiceDirectory eventhubs`. Set `EVENTHUBS_HOST` and `EVENTHUB_NAME`. Then run `AZURE_TEST_MODE=live cargo test --package azure_messaging_eventhubs --test '*'`. Each new test passes in live mode, and the tests pass when the full suite runs together.