Show genesis hash mismatches in plain words #1481

A hash mismatch error is printed as show output:

GenesisHashMismatch "./genesis.alonzo.spec.json" Mismatch (RelEQ) {supplied: "2418…", expected: "0000…"}

genesisReadErrorAt (File.hs#L466) and readByronGenesisConfig (Byron.hs#L51) turn the error into text with show, so callers can't print it better.

Wanted: plain words with the file and both hashes, e.g. the hash of ./genesis.alonzo.spec.json is 2418…, but the configuration gives 0000….

Originally posted by @carbolymer in #1475 (comment)