NSTextView: setting .font re-anchors the scroll view before your attribute edit runs

When you suppress AppKit auto-scroll during a whole-buffer attribute change (theme or zoom in a TextKit 1 NSTextView with non-contiguous layout), the font assignment itself also has to go inside the suppression. On a plain-text view, textView.font = x rewrites every character, and NSLayoutManager _resizeTextViewForTextContainer calls _scrollRangeToVisible:forceCenter: -> scrollToVisible, which moves the clip view by thousands of points. Pattern: capture a character + pixel-offset anchor, set a flag that makes your NSTextView subclass ignore scrollRangeToVisible/scroll(_:)/scrollToVisible(_:), do the edit, restore the anchor by scrolling the clip view directly, then clear the flag. Separately, when diffing attribute runs, comparing [Key: Any] values one by one with NSObject.isEqual was about 2x faster than bridging each dictionary to NSDictionary for isEqual(to:).