test: xnet from/to deleted cloud engine

[mraszyk]

No description provided.

[Copilot]

Pull request overview

Adds coverage for CloudEngine subnet deletion behavior when there are in-flight XNet messages, ensuring messages are rejected appropriately and that remaining stream data from the deleted subnet is not pulled.

Changes:

• Introduces a new XNet system test binary that deletes a CloudEngine subnet while messages are in flight and asserts expected reject codes.
• Adds a StateMachine-based analogue test that simulates the same scenario with a shared registry and mocked XNet layer.
• Wires the new tests into Cargo and Bazel build/test targets.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
rs/tests/message_routing/xnet/cloud_engine_subnet_delete_test.rs	New system test for CloudEngine subnet deletion with in-flight XNet messages.
rs/tests/message_routing/xnet/Cargo.toml	Adds dependencies and registers the new system test binary.
rs/tests/message_routing/xnet/BUILD.bazel	Adds Bazel system_test target for the new test binary and adjusts runtime deps.
rs/state_machine_tests/tests/mod.rs	Registers the new state machine test module.
rs/state_machine_tests/tests/cloud_engine_subnet_delete.rs	New StateMachine-based test exercising subnet deletion behavior.
rs/state_machine_tests/BUILD.bazel	Includes the new state machine test source in the integration test target.
Cargo.lock	Lockfile updates for the new/adjusted dependencies.

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