[ci] Migrate stress test and placement group compute configs to new schema

[sai-miduthuri]

Summary

Migrates 15 Anyscale compute config files from the legacy schema to the new SDK 2026 schema, and adds anyscale_sdk_2026: true to all corresponding test entries in release_tests.yaml.

Compute configs migrated (15 files)

Stress tests (release/nightly_tests/stress_tests/):

• stress_tests_compute.yaml / stress_tests_compute_gce.yaml
• stress_tests_compute_large.yaml / stress_tests_compute_large_gce.yaml
• smoke_test_compute.yaml / smoke_test_compute_gce.yaml
• stress_test_threaded_actor_compute.yaml
• placement_group_tests_compute.yaml / placement_group_tests_compute_gce.yaml
• stress_tests_single_node_oom_compute.yaml / stress_tests_single_node_oom_compute_gce.yaml

Placement group tests (release/nightly_tests/placement_group_tests/):

• compute.yaml / compute_gce.yaml
• pg_perf_test_compute.yaml / pg_perf_test_compute_gce.yaml

Tests updated in release_tests.yaml (9 tests)

1. stress_test_placement_group
2. stress_test_state_api_scale
3. stress_test_many_tasks
4. stress_test_dead_actors
5. threaded_actors_stress_test
6. stress_test_many_runtime_envs
7. single_node_oom
8. pg_autoscaling_regression_test
9. placement_group_performance_test

Schema changes applied

• cloud_id → cloud, ANYSCALE_CLOUD_ID → ANYSCALE_CLOUD_NAME
• head_node_type → head_node, worker_node_types → worker_nodes
• min_workers → min_nodes, max_workers → max_nodes
• use_spot: false → market_type: ON_DEMAND
• advanced_configurations_json / gcp_advanced_configurations_json → advanced_instance_config
• GCE: region + allowed_azs → zones
• Resources: cpu → CPU, gpu → GPU, flattened custom_resources
• Removed: region, max_workers, head/worker name fields (kept where multiple workers share instance type)
• Removed commented-out blocks
• Added CPU resources to head nodes where wait_for_nodes > worker count

Test plan

• All 15 config files validated against ComputeConfig.from_yaml()
• CI passes with anyscale_sdk_2026: true flag on all test entries

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request migrates several nightly and stress test compute configurations to a newer schema, likely associated with the Anyscale SDK 2026. Key changes include renaming configuration fields such as cloud_id to cloud, head_node_type to head_node, and worker_node_types to worker_nodes, as well as updating resource keys and market types. Additionally, the anyscale_sdk_2026: true flag has been enabled for these tests in release/release_tests.yaml. I have no feedback to provide.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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^{Reviewed by Cursor Bugbot for commit 8ed39cd. Configure here.}