LocalhostClusterTest: order lifecycle for smoother runs

[ReubenBond]

This pull request makes minor improvements to the LocalhostClusterTest method in LocalhostSiloTests.cs, focusing on code clarity and resource management order.

Test setup and cleanup improvements:

• Changed the array initialization for gateway ports to use the modern C# collection expression syntax for improved readability.
• Updated the startup sequence to start each silo and the client host sequentially rather than in parallel, which can help with error reporting and debugging.
• Reordered the shutdown and disposal calls for silos and the client host to ensure a more logical and consistent cleanup sequence.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR improves the LocalhostClusterTest method by modernizing syntax and establishing a more predictable lifecycle ordering for multi-silo cluster tests.

• Updated to use C# 13 collection expression syntax for array initialization
• Changed from parallel to sequential startup to improve debuggability and error reporting
• Reordered shutdown and disposal to follow proper Orleans cluster lifecycle (client first, then secondary silo, then primary silo)