…erform disposal after downstream operations have processed, rather than before, since the operator cannot guarantee that disposal is safe, when downstream consumers may still need to make use of these disposable items, in order to process removals.

Also fixed a bug within both versions of the `.SubscribeMany()` operator, where errors were not being properly propagated through the stream, and instead could bubble up to stream inputs.

Also fixed a bug within the cache version of `.MergeMany()` that allowed an internally-used subject to be disposed, without cleaning up all subscriptions that may later make use of it.

…any()` operators.