Replace uses of `BundleScratch` in the cloning code with `BundleWriter`

@chescock in https://github.com/bevyengine/bevy/pull/23808#discussion_r3093246344_ says:

If I'm reading this correctly, the only difference between `BundleWriter` and `BundleScratch` is that `BundleScratch` stores the `Bump` externally so it can rely on lifetimes a bit more for safety. Is that right? Will we want to do follow-up work to replace the uses of `BundleScratch` in the cloning code with `BundleWriter`?

Start by locating the cloning code that uses BundleScratch and read the BundleWriter and BundleScratch definitions, then review the discussion in PR #23808. Confirm whether the lifetime and external Bump distinction affects the replacement, and consider the work complete when the cloning code consistently uses BundleWriter without changing its behavior.

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