SCP-5054 Handle epoch-boundary block in chain-indexer tests

[bwbush]

I upgraded the marlowe-chain-indexer vs cardano-db-sync comparison test to account for epoch-boundary blocks (EBBs) on mainnet. I also added a comment in the PostgreSQL code noting the existence of EBBs.

The comparison tests at aff3683 passed (for blocks) and are recorded at http://testing.marlowe.run/database/. We still have unrelated comparison failures for mainnet only.

Pre-submit checklist:

• Branch
  • Tests are provided (if possible)
  • Test report is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
  • Relevant tickets are mentioned in commit messages
  • Formatting, materialized Nix files, PNG optimization, etc. are updated
• PR
  • Self-reviewed the diff
  • Useful pull request description
    • Review required
    • Substantial changes to code, test, or documentation
    • Change made to Marlowe validator (@bwbush and @palas must be included as reviewers)
    • Review not required
    • Minor changes to non-critical code, documentation, nix derivations, configuration files, or scripts
    • Formatting, spelling, grammar, or reorganization
  • Reviewer requested

[bwbush]

Reviewed in #493.