fix: honor requested num in IdentifyScaleInNodes

[ritesh-harihar]

Description
scale-in identification could return more nodes than requested, causing plugins to potentially drain/destroy too many nodes.

Problem
IdentifyScaleInNodes(cfg, num) was not enforcing the requested num consistently, which broke expected compatibility behavior for external plugins relying on this API.

Changes

• Ensure scale-in identification respects requested node count.
• Keep remote-check pre-scale-in behavior intact (identify eligible nodes, filter by remote IDs, then select).
• Add/extend regression coverage for:
  - honoring requested num
  - remote-check behavior
  - rejecting non-positive num inputs

JIRA ISSUE

Testing:

• validated via live Nomad test-setup flow + focused test suite.

• Previous flow:

• Current flow:

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.