[Grug] Add DeepEP profiling named scopes

[dlwh]

Add named scopes around DeepEP layout, dispatch/combine transport, local packing, and collapse paths so profiler traces can attribute movement and local work separately.

Part of #6139

[claude]

Claude finished @dlwh's task in 3m 41s —— View job

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Code review

No issues found. Checked for bugs and CLAUDE.md/AGENTS.md compliance.

This PR is purely additive profiling instrumentation — with jax.named_scope(...) wrappers around existing logic in lib/levanter/src/levanter/grug/_moe/ep_deepep.py. No control-flow, signature, or import changes; all reindentation lines up; import jax is already present; scope names follow the project's snake_case convention.

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