feat: adopt parentless queues under a synthetic default root queue

[gshaibi]

Description

This PR adds support for parentless queues (queues without a parent) by automatically adopting them under a synthetic __default__ root queue.

Changes

Core Logic (pkg/scheduler/cache/cluster_info/queue.go)

• A synthetic root queue named __default__ is now always created during queue snapshotting
• Parentless queues are automatically adopted under this root

Why __default__ instead of default?

To avoid potential conflicts with user-created queues named "default" (__default__ can't be created by users as it is not a valid resource name in Kubernetes)

Related Issues

Fixes #621

Checklist

Note: Ensure your PR title follows the Conventional Commits format (e.g., feat(scheduler): add new feature)

• Self-reviewed
• Added/updated tests (if needed)
• Updated documentation (if needed)

Breaking Changes

Additional Notes

[github-actions]

Merging this branch will decrease overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info	84.09% (-0.20%)	👎

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/queue.go	89.19% (-1.29%)	37 (-5)	33 (-5)	4	👎

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/cluster_info_test.go

[github-actions]

Merging this branch will decrease overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info	84.09% (-0.20%)	👎

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/queue.go	89.19% (-1.29%)	37 (-5)	33 (-5)	4	👎

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/cluster_info_test.go

[github-actions]

Merging this branch will decrease overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info	84.09% (-0.20%)	👎

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/queue.go	89.19% (-1.29%)	37 (-5)	33 (-5)	4	👎

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/cluster_info_test.go

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info	84.33% (+0.04%)	👍

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/queue.go	90.70% (+0.22%)	43 (+1)	39 (+1)	4	👍

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/cluster_info_test.go

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info	84.12% (+0.04%)	👍

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/queue.go	90.70% (+0.22%)	43 (+1)	39 (+1)	4	👍

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/NVIDIA/KAI-scheduler/pkg/scheduler/cache/cluster_info/cluster_info_test.go