Topdown lost commits

[cryptoAtwill]

Recover lost fendermint topdown commits from previous archived repo. Some major changes includes:

• Remove sync pointers that simplifies the polling logic
• Integrate with sync_many flag from main

Back then the requirement was only pushing the parent view to cache if the next block is a non-null block. In this case, we need to track:

1. The highest block pull (head)
2. The previous non-null block (tail)
   We were using a head and tail to pull data.
   Now we dont have this requirement, we just need the latest height fetched in cache to determine the next height to poll. The data is pushed to cache regardless if it's null or non-null. This way it simplifies the logic.

[aakoshh]

Great to see the code being simplified. Could you provide some description of what exactly changed? What replaces the pointers, why were they needed before but not any more?

[aakoshh]

LGTM, thanks!

I couldn't explain why it should be faster, though 🤔