Replace or fix multiformats library?

[dbluhm]

The multiformats library we're using has some issues that were reported back in May. The issue can be worked around by pinning typing-extensions to an older version but this workaround is causing some heartburn when it comes to solving dependency trees.

We should see if we can get this fixed or perhaps use another library.
Relevant issue: hashberg-io/multiformats#10

[dbluhm]

Attempted a fix in hashberg-io/typing-validation#2.