Fix pod memory request aggregation

[brendandburns]

Summary

• accumulate each container's memory request from the pod request total rather than the pod limit total
• add regression coverage using multiple containers with distinct memory requests and limits

This addresses the pod memory-request aggregation correctness gap identified in the client-go gap analysis.

Testing

• npm run build
• node --test --test-reporter=spec --import tsx src/top_test.ts
• repository push hooks

[cjihrig]

/lgtm
/approve

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: brendandburns, cjihrig

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