refactor: TestsetTable component code has been refactored

[ashrafchowdury]

Description
The TestsetTable component's code has been refactored to enhance code navigation and readability.

Major refactors:

• Sub-components have been separated from the TestsetTable component.
• Organized the code according to a standard format.
• Renamed the 'loading' useState to prevent confusion with the 'isLoading' hook.
• Enhanced the logic of the function.
• Introduced a new function called createNewColDefs to avoid code repetition.

Possible enhancements:

• Add a button to close the 'Unsaved changes' popup model for father changes.
• Automatically add a new column when the user deletes all existing columns from the table.
• Resolve the bug related to the drag-and-drop repositioning of columns, as I reported in issue [Bug]: Test set table columns position are not changing after drag-and-drop #1751

Issue
Closes #1764

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Name	Status	Preview	Comments	Updated (UTC)
agenta	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 7, 2024 0:23am

[bekossy]

Thank you for the PR @ashrafchowdury!