Avoid pipelining of future blocks

[bartfrenk]

Description

Supersedes #4310.

Updates chain selection to first check for blocks from the future before setting the tentative header. This avoids pipelining blocks from the future.

• 1bc9135 by @nfrisby.
• Testing to ensure future blocks are not emitted to followers.

Checklist

• Branch
  • Commit sequence broadly makes sense
  • Commits have useful messages
  • New tests are added if needed and existing tests are updated
  • Any changes affecting Consensus packages must have an entry in the appropriate changelog.d directory created using scriv. If in doubt, see the Consensus release process.
• Pull Request
  • Self-reviewed the diff
  • Useful pull request description at least containing the following information:
    • What does this PR change?
    • Why these changes were needed?
    • How does this affect downstream repositories and/or end-users?
    • Which ticket does this PR close (if any)? If it does, is it linked?
  • Reviewer requested