sglang: bump to 0.5.19 + DeepEP v2 over EFA (amzn2023)

[jinyan-li1]

Bumps the SGLang amzn2023 image to sglang 0.5.19 and integrates DeepEP v2 over EFA, mirroring the vLLM and vLLM-Omni amzn2023 images.

• sglang 0.5.17 → 0.5.19 (torch 2.13, sgl-kernel 0.4.6.post1, flashinfer 0.6.18, mooncake 0.3.13, cutlass-dsl 4.6.2)
• DeepEP v2 from the amazon-contributing/DeepEP fork; NCCL 2.31.2 (cu13), runtime-pinned with a version assert
• EFA 1.50.0, GDRCopy 2.5.2
• Prebuild all_reduce_perf so the EFA test setup is a no-op
• DeepEP-v2 sanity check (deep_ep present + runtime NCCL >= 2.30.4)
• dlc_minor_version 3 → 4

Draft — validating in CI.