Refactor around ConwayMempoolFailure, for Dijkstra

[nfrisby]

ConwayMempoolFailure is part of the longstanding PredicateFailure. The analogous Disjkstra.MempoolFailure is not. This Issue anticipates that Dijkstra integration will therefore require some rearranging of at least the LocalTxSubmission mini protocol, some mempool tracer events, etc.

I think this is the relevant cardano-ledger PR IntersectMBO/cardano-ledger#4890

[nfrisby]

Ah, I think this line (in our code) is still fine. type instance ApplyTxErr (ShelleyBlock proto era) = SL.ApplyTxError era. It's the upstream definition of SL.ApplyTxError that changed.

$ git grep -e 'type ApplyTxError' -- '*hs'
eras/shelley/impl/src/Cardano/Ledger/Shelley/API/Mempool.hs:newtype ApplyTxError era = ApplyTxError (NonEmpty (PredicateFailure (EraRule "LEDGER" era)))
$ git grep -e 'data ApplyTxError' origin/master -- '*hs'
origin/master:eras/shelley/impl/src/Cardano/Ledger/Shelley/API/Mempool.hs:  data ApplyTxError era

So maybe the LocalTxSubmission doesn't need to change at all. But any code that "opens" an SL.ApplyTxError without specific era will need to change (eg in #1831).