FIX (kubernetes): align accelerator dict keys during scaling (#7100)

[pravarpathania]

Problem

sky show-gpus --infra k8s fails with:
AssertionError: Keys of counts ([]), capacity ([]), and available (['L4']) must be the same.

This occurs during Kubernetes cluster scaling (e.g., when a GKE GPU node pool is resizing).
Accelerators are discovered via node labels before their status.allocatable field reports capacity or availability, leading to mismatched accelerator dictionary keys.

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Change

• sky/catalog/kubernetes_catalog.py: Added key alignment logic to ensure counts, capacity, and available dictionaries always share the same keys.
• sky/core.py: Improved assertion message to include contextual information for easier debugging.
• tests/unit_tests/kubernetes/test_kubernetes_utils.py: Added comprehensive test cases covering:
  • Nodes scaling with 0-capacity accelerators
  • Mixed ready + scaling nodes
  • Edge scenarios with transient GPU states

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Why

• Prevents sky show-gpus --infra k8s from crashing during cluster scaling operations.
• Handles transient Kubernetes states gracefully.
• Improves robustness and error transparency for GPU discovery.
• Platform-agnostic — while first reported on GKE, this fix applies to any Kubernetes environment (EKS, AKS, on-prem, etc.).

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Tested

• Unit tests: pytest tests/unit_tests/kubernetes/test_kubernetes_utils.py
• All catalog-related tests: pytest tests/unit_tests -k catalog
• Pre-commit formatting and linting (pre-commit run --files <changed-files> or ./format.sh <changed-files>)
• Edge cases simulated (scaling-only, mixed-node clusters, no accelerators)

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Files Modified

• sky/catalog/kubernetes_catalog.py
• sky/core.py
• tests/unit_tests/kubernetes/test_kubernetes_utils.py

Fixes:

• Fixes [UX] sky show-gpus --infra k8s fails during the kubernetes cluster GPU node pool is scaling up #7100

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Notes

• This branch rebases on the latest upstream/master to ensure a clean, up-to-date diff.

• Code formatting: install pre-commit (auto-check on commit) or bash format.sh

• Any manual or new tests for this PR (please specify below)

• All smoke tests: /smoke-test (CI) or pytest tests/test_smoke.py (local)

• Relevant individual tests: /smoke-test -k test_name (CI) or pytest tests/test_smoke.py::test_name (local)

• Backward compatibility: /quicktest-core (CI) or pytest tests/smoke_tests/test_backward_compat.py (local)