`allowNestedScroll` should smooth-scroll nested containers, not fall back to native

Problem

allowNestedScroll: true detects nested scrollable containers and yields to their scroll, but the nested scroll itself is native, no Lenis momentum/inertia. The page scrolls smooth, inner containers (e.g. a max-height table) scroll with browser-default jank.

The workaround is manually instantiating a child Lenis per container with overscroll: true and a virtualScroll boundary callback (#259, #391). This works but is boilerplate every user has to replicate.

allowNestedScroll imho sets the expectation that nested scroll is handled.