refactor(KeepAlive): scope wrapChildren props, drop as any in getExisting

[chiefcll]

Summary

Two small cleanups to src/primitives/KeepAlive.tsx. No behavior change.

1. Stop leaking KeepAlive-level config onto the Lightning view

wrapChildren did:

<view
  {...props}
  preserve
  onRemove={onRemove}
  onRender={onRender}
  forwardFocus={0}
  transition={transition}
/>

props is s.ParentProps<KeepAliveProps>, so the spread also pushed id, shouldDispose, and the original unchained onRemove / onRender / transition onto the view before the targeted overrides re-set them. Harmless for id, but shouldDispose is purely KeepAlive-level — it has no business landing on a Lightning element. Replace the spread with explicit props the view needs and insert props.children directly.

2. Reflect that KeepAliveElement is populated lazily

getExisting constructs a partial entry holding only id + the isAlive signal, and only populates owner / children / dispose once the route mounts or preload runs. Today the type marks those three fields as required, and getExisting resorts to as any. Mark them optional on KeepAliveElement (matching reality), drop the cast, and tighten the existing casts at call-sites to as unknown as ElementNode | undefined so optional chaining can work honestly.

Test plan

• tsc --noEmit clean (pre-existing errors elsewhere in the repo are unaffected).
• eslint src/primitives/KeepAlive.tsx clean.
• Manual: KeepAlive + KeepAliveRoute mount/unmount/back-nav cycles unchanged.

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