Prevent DeepCloneFrom self-clone from clearing collections

[Copilot]

DeepCloneFrom previously cleared the destination before enumeration, which silently emptied data when dest and source were the same instance. This broke the intended in-place clone pattern (collection.DeepCloneFrom(collection)).

• Core fix (collection + dictionary overloads)

  • Snapshot source items before Clear() in:
    • DeepCloneFrom<T>(ICollection<T> dest, IEnumerable<T> source)
    • DeepCloneFrom<TKey, TValue>(IDictionary<TKey, TValue> dest, IDictionary<TKey, TValue> source)
  • This preserves original elements for cloning even when source and destination reference the same object.

• Regression coverage

  • Added focused tests for same-instance in-place cloning:
    • DeepCloneFrom_SameCollectionInstance_ShouldPreserveAndCloneItems
    • DeepCloneFrom_SameDictionaryInstance_ShouldPreserveAndCloneItems
  • Tests assert both data preservation and replacement with deep-cloned element instances.

T[] items = [.. source];
dest.Clear();
foreach (T? item in items)
{
    dest.Add(DeepClone(item));
}

• Fixes DeepCloneFrom empties the destination when dest and source are the same collection instance #64

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud