🐞 Programmatic cursor state updates are never applied

### Description

Programmatic updates to `SourceEditorState.cursorPositions` are never applied to the underlying `TextViewController`.

In `SourceEditor.updateControllerWithState(_:controller:)`, the new cursor positions are compared with the same state value:

```swift
if let cursorPositions = state.cursorPositions, cursorPositions != state.cursorPositions {
controller.setCursorPositions(cursorPositions)
}
```

Because `cursorPositions` was just unwrapped from `state.cursorPositions`, the comparison is always false.

### To Reproduce

1. Create a `SourceEditor` with a binding to `SourceEditorState`.
2. After the editor appears, programmatically assign a different value to `state.cursorPositions`.
3. Observe that the editor cursor does not move to the requested position.

### Expected Behavior

Changing `SourceEditorState.cursorPositions` should update the cursor positions in the underlying controller.

The comparison likely needs to use the controller's current state:

```swift
if let cursorPositions = state.cursorPositions,
cursorPositions != controller.cursorPositions {
controller.setCursorPositions(cursorPositions)
}
```

### Version Information

CodeEditSourceEditor: main, revision 1fa4d3c
macOS: 15.7.9
Xcode: 26.3 (17C529)

### Additional Context

No matching open or closed issue was found before filing this report.

### Screenshots

Not applicable.

从 SourceEditor.updateControllerWithState(_:controller:) 开始，检查 state.cursorPositions 如何与 controller 当前的光标位置进行比较。重现 issue 中描述的 binding 更新，然后验证为 SourceEditorState.cursorPositions 赋予不同的值会移动底层 TextViewController 的光标。

由索引模型根据 Issue 内容生成。