[sglang] feat: Support SGLang remote_instance

[EduardDurech]

Support SGLang remote_instance as well as different {rank0,k-ary,epidemic} seed strategies

Requires sgl-project/sglang#16410

[gemini-code-assist]

Code Review

This pull request introduces support for SGLang's remote_instance feature, enabling more efficient distributed model weight loading. It adds a RemoteInstanceSeedCoordinator Ray actor to manage seed replicas and supports various seeding strategies (rank0, k-ary, epidemic). The changes are well-structured, including new port management utilities and updates to the server launch logic. The implementation correctly uses a lease-like mechanism for seed servers, with a finally block to ensure they are returned. However, I've identified a high-severity issue in the error handling within this finally block, which could lead to resource leaks and potential deadlocks.