Update `BlockStreamer` return type

[dlachaume]

Content

This PR includes a modification of the BlockStreamer trait to be able to handle rollbacks.

Pre-submit checklist

• Branch
  • [ ] Tests are provided (if possible)
  • [x] Crates versions are updated (if relevant)
  • [ ] CHANGELOG file is updated (if relevant)
  • [x] Commit sequence broadly makes sense
  • [x] Key commits have useful messages
• PR
  • [x] No clippy warnings in the CI
  • [x] Self-reviewed the diff
  • [x] Useful pull request description
  • [x] Reviewer requested
• Documentation
  • [ ] Update README file (if relevant)
  • [ ] Update documentation website (if relevant)
  • [ ] Add dev blog post (if relevant)

Issue(s)

Closes #1704

[github-actions[bot]]

Test Results

    3 files  ±0     43 suites  ±0   8m 31s :stopwatch: -7s   991 tests ±0    991 :white_check_mark: ±0  0 :zzz: ±0  0 :x: ±0  1 089 runs  ±0  1 089 :white_check_mark: ±0  0 :zzz: ±0  0 :x: ±0 

Results for commit 06ce18ea. ± Comparison against base commit 1dd6495d.

:recycle: This comment has been updated with latest results.