2 * X queries vs. 1

currently a single transaction with a batch X of documents does 2 * X SQL queries.
it looks whether the document exists first and then inserts or updates it:

(defrecord JdbcDocumentStore [ds dbtype]
  db/DocumentStore
  (submit-docs [this id-and-docs]            ;;    batch of documents
    ;; ...
    (doseq [[id doc] id-and-docs
      (if-not (do

It would be better and easier to debug a program if the BytesEncoding and BytesDecoding traits could return any error type.

To do so we need to modify the Error enum and more specifically the Encoding and Decoding variants to wrap a Box<dyn Error>.