chore(data-grid): rename variables (#1119)

* refactor(data-grid): rename cols to columnCount for clarity

Co-authored-by: Cursor <cursoragent@cursor.com>

* refactor(data-grid): use consistent Count suffix for all tab/column variables

Co-authored-by: Cursor <cursoragent@cursor.com>

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Co-authored-by: Cursor <cursoragent@cursor.com>

Author: sadmann7