fix(plugin): expose backend ops required by TP comm overlap

[lihongyang1990]

Summary

• register device_supports_multicast, ubuf_built_with_mpi, and get_stream_priority_range for the CUDA and Hygon plugin backends
• forward the runtime queries to each native backend extension
• convert CommOverlapType to the native backend enum before creating CommOverlapP2P

Problem

When tp_comm_overlap: true is enabled, user-buffer initialization calls these runtime helpers through the TE-FL plugin interface. The CUDA and Hygon implementations were not exposed in the operator registry, which caused missing-function errors before TP communication overlap could initialize.

Validation

• compiled all four changed Python modules
• git diff --check