Write specification for bao blob sync protocol

[rklaehn]

basically write a spec for iroh-bytes that would allow somebody to do a clean room impl of the protocol.

this should be a textual spec, a generator of examples, and a number of handcrafted/curated examples.

[rklaehn]

This https://github.com/n0-computer/iroh/pull/1402 is at least a start...

What would be needed in addition would be

• [ ] a byte level spec (that can refer to the postcard spec)
• [ ] a number of tests that work on a byte level, that other implementers could copy into their impls, with byte level explanation
• [ ] a generator that can produce an arbitrary number of request and response blobs for people to test their impls with

Idea for the generator:

it produces a directory containing a number of blobs, like this:

<hash1>.data
<hash2>.data

and a number of request/response pairs that can be satisfied with the data in the directory:

<testnr>.request
<testnr>.response

Basically: given the files *.data, when given <x>.request, I have to produce exactly the bytes in <x>.response. Then I have a compatible impl. There is zero leeway here - everything should be completely deterministic.

This generator should be able to produce arbitrarily much test data.

[rklaehn]

https://github.com/n0-computer/iroh/pull/1407 is the way the wire level tests would be written...