`guppy retrieve` error: maximum agent message header size exceeded

[volmedo]

I got this error when trying to reproduce the issue in #353

FATAL	main	guppy/main.go:29	opening path in retrieved filesystem: failed to get root node: locating block bafybeihbqlesvtrimzm7jf5sg2am6slphdwgc53oagfd7l2ofljemfzcva: querying claims for [zQmdWx7HVRte4aHD475a318KZU9hmHuUFmz2o5KVoMZnJdM]: encoding X-Agent-Message header: maximum agent message header size exceeded

The root cause is that guppy attaches to the delegation all the relevant proofs in its delegation store. These proofs often form several valid chains, and including only one of such chains would be enough for the delegation to work.

The approach to fix has been to add new functionality to go-ucanto's validator to allow clients to validate chains as servers do. The result of the process is a valid chain that contains only the required proofs. This functionality is used when issuing a new delegation if the new WithOptimizeProofChain option is enabled.