test: verify broker properties update reconciliation

[pavanvishnusai]

What this PR does / why we need it:

Strengthens the Agent reconciliation unit test for existing discovery requests.

Previously, test_reconcile_nothing_to_do only verified that set_extra_device_properties() was called. This update verifies that the method receives the broker properties from the updated ConfigurationSpec.

This helps cover the reconciliation path where an existing discovery request should receive updated broker properties from the Akri Configuration.

Special notes for your reviewer:

This is a test-only change. No production behavior is changed.

Testing:

• rustfmt agent/src/util/discovery_configuration_controller.rs --edition 2021 --check
• Attempted cargo test -p agent test_reconcile_nothing_to_do, but local macOS build is blocked by the Linux-only libudev system dependency.

If applicable:

• this PR has an associated PR with documentation in akri-docs
• this PR contains unit tests
• added code adheres to standard Rust formatting (rustfmt agent/src/util/discovery_configuration_controller.rs --edition 2021 --check)
• code builds properly (cargo build)
• code is free of common mistakes (cargo clippy)
• all Akri tests succeed (cargo test)
• inline documentation builds (cargo doc)
• all commits pass the DCO bot check by being signed off -- see the failing DCO check for instructions on how to retroactively sign commits