chore: update the chain follower logs to report validation

[akaladarshi]

Summary of changes

Changes introduced in this pull request:

• Instead of the max forks epoch remaining to start validation, now log shows min epochs remaining to start validation
• Update the chain follower logs to report the remaining tipset to start validation instead of remaining downloads

Reference issue to close (if applicable)

Closes #5499

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• This pull request is based on an issue that a maintainer has accepted (see Before Opening a Pull Request).
• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

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