build(container): backport EFA build fixes (#9705, #9727) to release/1.2.1

[jh-nv]

Summary

Cherry-pick of two EFA container build fixes from main to release/1.2.1:

• build(container): bump nixl_gdrcopy_ref to v2.5.2 (kernel >=6.15 fix) #9705 — build(container): bump nixl_gdrcopy_ref to v2.5.2 (kernel >=6.15 fix)
• feat(container): configurable libfabric repo + v2.5.1 overlay for EFA #9727 — feat(container): configurable libfabric repo + v2.5.1 overlay for EFA

Together these fix the Dynamo EFA container build (GDRCopy kernel ≥6.15 compatibility, configurable libfabric repo, and the libfabric v2.5.1 overlay needed for the EFA RDMA path).

Original PRs

• build(container): bump nixl_gdrcopy_ref to v2.5.2 (kernel >=6.15 fix) #9705 — merge commit fffea8cb4e0916fb35fc8491839cba893353180c
• feat(container): configurable libfabric repo + v2.5.1 overlay for EFA #9727 — merge commit d515c5f8c78cbacdda1e67616cf4836ce0a29968

Conflicts resolved

Cherry-pick of #9727 conflicted in two files; resolved as follows:

• container/context.yaml — took the incoming side (configurable nixl_libfabric_repo + nixl_libfabric_ref: v2.5.1); this is the core of the fix.
• container/templates/wheel_builder.Dockerfile — combined both sides: kept release branch's git yasm (needed for the ffmpeg/libvpx build present on 1.2.x) and added feat(container): configurable libfabric repo + v2.5.1 overlay for EFA #9727's --setopt=tsflags=nocontexts.

#9705 applied cleanly.

Test plan

• CI passes
• EFA container build succeeds (libfabric v2.5.1 + GDRCopy v2.5.2)

🤖 Generated with Claude Code

[dynamo-ops]

Review: backport of EFA build fixes to release/1.2.1

The diff is clean. Cherry-picks of #9705, #9727, and #10047 applied correctly to the release branch. Conflict resolution in wheel_builder.Dockerfile (keeping yasm + adding --setopt=tsflags=nocontexts) is correct.

Two minor notes:

1. PR description lists #9705 + #9727 only, but the actual diff includes #10047 (libfabric2.5.1 for EFA and TRTLLM) as well — the rm -rf /opt/amazon/efa && cp -Pfr replacement approach and the trtllm NIXL plugin block are from that PR. Consider updating the description for traceability.

2. Dead exports in trtllm RUN block (cosmetic, non-blocking):

   export LD_PRELOAD=/opt/nvidia/nvda_nixl/lib64/libnixl.so && \
   export NIXL_PLUGIN_DIR=/opt/nvidia/nvda_nixl/lib64/plugins && \

   These have no effect inside RUN (the ENV statements below handle persistence). Could be removed to reduce confusion, but not a real issue since they match the subsequent ENV values.

[dynamo-ops]

Previous review comments have been addressed. Approving.

[saturley-hall]

Test failures are unrelated to change.