Fix bug with being unable to deserialise parties resulting in fatal error

[noonio]

As part of #1282 we noticed that 0.19 on preprod is, we think, trying to deserialise a party key -

hydra/hydra-tx/src/Hydra/Tx/Crypto.hs

Line 152 in 696a4a0

maybe (error "TODO: SerialiseAsRawBytesError, but constructor not exported") (Right . HydraVerificationKey) (rawDeserialiseVerKeyDSIGN bs)

- and hits the error case there.

Because it's an error, it entirely crashes the Hydra process, and prevents the chain-observer from being able to make observations.

Perhaps we need to represent "invalid" head states like this one a bit more explicitlly; i.e. it's still a Hydra head, but with an unparseable head participant.

Options:

• Just drop the unparsable party, instead of crashing (and at least log an error instead of dieing entirely),
• Represent unparsable parties differently; i.e. data Party = ValidParty Party | BadParty ....
• Represent the entire head state differently, if one of the parties fails parsing ...
• ???

Context

This error was observed with the 0.19 hydra-chain-observer and deployed from this commit over on the hydra-explorer repo - docker-compose,yaml @ relevant version.

In particular it was observed through docker logs ... of the relevant image; and even more in particular docker logs prints any errors it sees to stderr`; so you can get all the relevant information like:

docker logs hydra-explorer-hydra-chain-observer-preprod-0.19-1 >logs.txt 2>&1

[ch1bo]

We don't know whether it is a head transaction that was tried to parse!

• Not use error -> Yes
• Changing Party data type -> No

@noonio can you include steps to reproduce please? i.e. which commit, which binary, how we observed this.