PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/DevelopmentWorkflow.md#running-unit-tests-application.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

When destroying a reusable view's node, two issues exist:

1. destroyNode() calls callUnloaded() unconditionally, even when the view was never loaded. This can fire unloaded lifecycle events (and run unload logic) on views that are not in a loaded state.
2. During _tearDownUI(), children are torn down by inheriting the parent's force flag (child._tearDownUI(force)). When the parent is being destroyed but a child is marked as reusable, the child's native view is preserved and skipped, leaving orphaned/leaked native views behind.

What is the new behavior?

1. destroyNode() now uses unloadView(this), which guards on view.isLoaded before calling callUnloaded(), so the unloaded path only runs for views that are actually loaded.
2. When a view is torn down, its children are now always torn down with force = true (child._tearDownUI(true)), regardless of whether they are marked reusable. Once a parent is being destroyed, its children are destroyed too. Developers who want to reuse a child elsewhere are responsible for detaching it beforehand.

Together these changes make the teardown process for reusable views more correct and prevent native view leaks.