Release dataset after training and optimization

[zhenghaoz]

No description provided.

[Copilot]

Pull Request Overview

This PR refactors dataset management to release datasets after training and optimization. The primary goal is to improve memory management by restructuring how datasets are stored and accessed within the Master struct.

• Moved dataset fields from Master struct to a new Datasets struct that's returned from loadDataset()
• Modified the loadDataset() function to return a Datasets struct instead of individual dataset pointers
• Removed dataset storage fields and related mutexes from the Master struct

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
master/master.go	Introduces new Datasets struct and removes dataset storage fields from Master struct
master/tasks.go	Refactors loadDataset() to return Datasets struct and updates all dataset references
master/tasks_test.go	Updates test cases to work with new dataset structure and removes assignments to removed struct fields

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