ReplaceWith empties the collection when the new items are derived from the collection itself #132

What's wrong

CollectionExtensions.ReplaceWith (Extensions/CollectionExtensions.cs, ~line 65) clears the collection before reading newItems. When newItems is a lazy query over the same collection, or the collection itself, it is read after the clear and yields nothing.

Repro

var list = new List<int> { 1, 2, 3, 4 };
list.ReplaceWith(list.Where(x => x > 2));
// list is [] — expected [3, 4]

var list2 = new List<int> { 1, 2, 3 };
list2.ReplaceWith(list2);
// list2 is [] — expected [1, 2, 3]

Reproduced against the current main build.

Why it matters

"Replace the contents with a filtered, sorted or projected version of themselves" (items.ReplaceWith(items.Where(...)), items.ReplaceWith(items.OrderBy(...))) is the most natural use of this helper, for example on an ObservableCollection bound to a UI where the instance must be kept. It silently wipes the data with no exception.

Suggested fix

Materialize the new items before clearing:

T[] snapshot = [.. newItems];
collection.Clear();
foreach (T item in snapshot) collection.Add(item);

Acceptance criteria

• Both repro cases produce the expected contents.
• Regression tests for a lazy self-query and for self-replacement.