Add lighter version of can_clone_instance from 35919a0

[jamesray1]

PR summary

I just want to test as per #1782. Edit: I can get cargo build in the nix-shell to run without freezing my laptop, so don't need to do this.

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followups

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- summary of change [PR#1234](https://github.com/holochain/holochain-rust/pull/1234)

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