Add HTML repr for Image and Subject

[fepegar]

Checklist

• I have read the CONTRIBUTING docs and have a developer setup ready
• Changes are
  • Non-breaking (would not break existing functionality)
  • Breaking (would cause existing functionality to change)
• Tests added or modified to cover the changes
• In-line docstrings updated
• Documentation updated
• This pull request is ready to be reviewed

[fepegar]

@copilot fix the CI errors

[Copilot]

@fepegar I've opened a new pull request, #1405, to work on those changes. Once the pull request is ready, I'll request review from you.