clarifying the script integrity hash

[JaredCorduan]

Description

Clarifying the script integrity hash in the CDDL description:

• remove the outer square brackets so as to not imply that the bytes are inside of a CBOR array
• explicitly describe in prose that we are concatenating
• use the notation from cryptography of double pipe for concatenation
• make it clear that if there are no datums, that "empty string" here means the empty bytestring, ie that it is omitted.

Checklist

• Commit sequence broadly makes sense
• Commits have useful messages
• New tests are added if needed and existing tests are updated
• Any changes are noted in the changelog
• Code is formatted with fourmolu (which can be run with scripts/fourmolize.sh)
• Cabal files are formatted (which can be done with scripts/cabal-format.sh)
• Self-reviewed the diff

[teodanciu]

Looks good to me

[JaredCorduan]

The CI failure was the inability to generate a sufficiently long trace for a small-step-semantics test. I am unworried about this and will re-run.