fix(worker): omit empty topology config

[crliu3227]

Summary

Fixes Worker registration failures when no Slurm topology is configured.

The operator previously emitted an empty Topology= entry in slurmd --conf.
When the container entrypoint appended CoreSpecCount and MemSpecLimit, Slurm
parsed CoreSpecCount as the topology value and marked the node as
INVALID_REG.

Changes

• Do not emit Topology= unless topology is explicitly configured through
  NodeSet.spec.extraConf.
• Remove the unused SLINKY_TOPOLOGY environment variable.
• Preserve explicit Topology=<value> configuration through extraConf.
• Keep topology synchronization through the Slurm API after node registration.
• Add regression coverage for the default --conf output.
• Update the architecture documentation.

Result

Workers without topology now register with resource configuration similar to:

--conf Features=slinky CoreSpecCount=36 MemSpecLimit=175607
This allows Slurm to correctly report the configured effective CPU and memory
resources.
Testing
go test -mod=mod ./internal/builder/...
go test -mod=mod ./internal/builder/workerbuilder

Fixes SlinkyProject/containers#20

[vivian-hafener]

Good morning @crliu3227,

I am looking into this. I believe that the issue reported in SlinkyProject/containers#20 could be resolved more simply via a change to the slurmd-entrypoint file logic in the containers repo, instead of a change to operator. I am pursuing that option via an internal MR. Once I have confirmed that my resolution resolves your issue, I will close this MR.

Best,
Vivian Hafener

[vivian-hafener]

I have an internal MR to https://github.com/SlinkyProject/containers that resolves this. I will update SlinkyProject/containers#20 with the commit ID once that is merged.