[ImmutableSet] Optimize add/remove operations to avoid redundant tree modifications (#159845)

Optimize ImmutableSet operations to avoid unnecessary tree modifications
when adding existing elements or removing non-existent elements.

- Modified `ImutAVLFactory::add_internal()` to return the original tree
when both key and value are the same, avoiding unnecessary node creation
- Updated `ImutAVLFactory::remove_internal()` and `add_internal()` to
return the original tree when no changes are made.

Note that `balanceTree` always end up creating at least one node even
when no rebalancing is done. So we also need to avoid unnecessary calls
to it.