Support Hash Function Negotiation

[softwareplumber]

The two sides of a transfer need to agree on which hash functions they support. XXH3 is defined as the canonical hash for Car mirror bloom filters, but some sites with hardware acceleration for a particular hash algo may want to use a different option. Also Kubo itself creates a bloom to accelerate Has checks on its local block store - we can't dictate which hash function is used for this, so being able to share that data requires some element of hash negotiation.

ETA: 2024-06-30