feat: No copy.

[saul-jb]

It would be cool if this lib had a nocopy option like Kubo has. The no copy in Kubo uses the filestore spec.

I believe this requires a special blockstore implementation, so I have made one here: ipfs/js-stores#233

[achingbrain]

This can be implemented by a no-copy blockstore as you've found, so there's nothing to do here.

That said, the problem with nocopy is other processes changing the imported files behind the back of the blockstore which I don't think Kubo ever came up with a solution for.