Selected param on Choice elements is ignored when parent Choices tag is set to perRegion

**Describe the bug**
When using the Choices tag with `perRegion="true"` attribute, the `selected="true"` attribute on individual Choice elements is ignored. This means that default selections don't work properly when labeling regions, forcing users to manually select options each time.

**To Reproduce**
Steps to reproduce the behavior:
1. Create a Label Studio project with a configuration that includes Choices with `perRegion="true"`
2. Add selected="true" to one of the Choice elements within the choice group
3. Start labeling and create a region
4. Notice that none of the choices are pre-selected, despite having the selected="true" attribute.

Example configuration demonstrating the issue:
```xml

```

**Expected behavior**
When creating a new region, the Choice element with `selected="true"` should be automatically selected by default. This would save time for annotators who frequently use the same choices.

**Screenshots**

**Environment (please complete the following information):**
- OS: macOS Sequoia 15.3.2
- Label Studio Version: 1.17.0