[mridul-sahu]

Title: Add n2-highmem and more n2-standard CPU device types

Adds CPU device types for n2-highmem-{2,4,8,16,32,48,64,96} and n2-standard-{8,16,48,96}, following #1128 (n2-standard-4). Entries are generated by get_cpu_system_characteristics_map (like the TPU helper) for VM counts 1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 128, 160, 256, 320, 512, 640: powers of two and 5 × powers of two, at most 1,000 (GKE's nodes per node pool and zone). Existing CPU entries are unchanged.

Motivation: running many simulated TPU hosts per VM needs high-memory or mid-size machines and non-power-of-two VM counts.

Testing: unit tests for the helper and catalog lookups; make run-unittests 513 passed; pyink/pylint/mypy clean. Used end to end (as a runtime catalog patch) for cluster create and workload create with n2-highmem-8-320 and n2-highmem-4-640 on GKE.

[gemini-code-assist]

Code Review

This pull request expands the supported CPU machine types in XPK by adding several n2-highmem and n2-standard configurations. It introduces a helper function get_cpu_system_characteristics_map to dynamically generate CPU device types for various VM counts, updates the documentation and README to reflect these additions, and includes comprehensive unit tests to verify the new behavior. No review comments were provided, so I have no feedback to evaluate.