SCHED-962: Set finite default SuspendTime for Slurm power-save

[Uburro]

Problem

SuspendTime=-1 maps to Slurm INFINITE, which disables power-save when partitions do not define their own finite SuspendTime. As a result, scontrol power down <node> cannot trigger SuspendProgram for ephemeral nodes.

Solution

Changed the default SuspendTime to 1000000000, a large finite value that keeps Slurm power-save enabled while effectively avoiding automatic idle power down in normal operation. Updated the CRD documentation and added a render test for this value.

Testing

Manually on the live cluster
Ran:

go test ./internal/render/common

Release Notes

Changed the default Slurm SuspendTime to a large finite value so ephemeral node power-save commands can trigger SuspendProgram reliably. No migration is required; users can still override spec.slurmConfig.suspendTime explicitly.