Propagate exclude_nodes to all get_nodes_by_spec callers (nemo-run, nemo-launcher, single-sbatch-runner, and others)

[coderabbitai]

Background

PR #830 introduced the exclude_nodes parameter to SlurmSystem.get_nodes_by_spec() and wired it through the Megatron-Bridge command generation strategy. However, several other workloads and infrastructure components call get_nodes_by_spec() directly without forwarding test_run.exclude_nodes, so the exclusion has no effect for those paths.

Affected call sites

The following production code locations call get_nodes_by_spec() without passing exclude_nodes:

File	Line	Caller context
src/cloudai/workloads/nemo_run/slurm_command_gen_strategy.py	126	NeMo-Run command gen
src/cloudai/workloads/nemo_launcher/slurm_command_gen_strategy.py	40	NeMo-Launcher command gen
src/cloudai/workloads/triton_inference/slurm_command_gen_strategy.py	86	Triton Inference (_get_server_client_split)
src/cloudai/workloads/deepep/slurm_command_gen_strategy.py	90	DeepEP command gen
src/cloudai/workloads/ai_dynamo/slurm_command_gen_strategy.py	206	AI Dynamo command gen
src/cloudai/systems/slurm/slurm_command_gen_strategy.py	325	Base Slurm strategy (_enable_vboost_cmd)
src/cloudai/systems/slurm/single_sbatch_runner.py	95, 118	Single-sbatch runner (node list aggregation and per-test-run node resolution)

Required changes

For each call site above:

1. Parse test_run.exclude_nodes (a comma-separated string) into a set[str] using parse_node_list (already available in slurm_system.py), consistent with how SlurmCommandGenStrategy does it in this PR.
2. Pass the resulting set as exclude_nodes=... to get_nodes_by_spec().
3. For single_sbatch_runner.py, collect and union all exclude_nodes values across the test runs being batched.

Priority

Low — this is a follow-up to PR #830; existing behaviour (no exclusion) is preserved until these sites are updated.

References

• PR: Megatron-Bridge r0.3.0 enhancement #830
• Comment: Megatron-Bridge r0.3.0 enhancement #830 (comment)