Fix isolate outer si typing

[wclr]

• There exists an issue discussing the need for this PR
• I added new tests for the issue I fixed or built
• I used pnpm run commit instead of git commit

  const X = (s: { DOM: MainDOMSource }) => {
    return {
      DOM: xs.of(img()),
    }
  }

const IsolatedX = isolate(X)
const x =  IsolatedX({ DOM })
// now x.DOM  is Stream<VNode> instead of Stream<any>
x.DOM.map((vnode) => vnode.children) 

[wclr]

The with isolate with typings also refers to staltz/xstream#306
as I'm using a distinct version of MemoryStream type which Stream is not assignable to.

@staltz
So I'm not proposing to merge this PR as there may be other issues related to this, but want to draw your attention, to that isolate tyings actually does not work correctly now and using explicit any in public API like here, in this case, is not a very good thing.

PR #949 actually fixes this issue with isolating DOM sink with current DOM driver without need of this PR.