feat(epoch-sync): implement function to extend epoch sync proof by one epoch

[shreyan-gupta]

This PR adds the core functionality of adding the function extend_epoch_sync_proof.

While at it, the function derive_epoch_sync_proof_from_last_final_block is also updated to take the last_block_hash as parameter instead of next_block_header_after_last_final_block_of_current_epoch.

There is some refactoring involved for the function derive_epoch_sync_proof_from_last_final_block to reuse some of the functions between itself and extend_epoch_sync_proof but there should be functionality or logic change for derive_epoch_sync_proof_from_last_final_block.

This PR requires careful review.

For testing these changes I plan to do the following in follow up PRs

• Write a test loop test to verify the extend epoch sync proof functionality. A part of it is already implemented in master...shreyan/epoch-sync/all-changes
• Add a debug assert that verifies the extended proof is the same as the proof generated from scratch. Over time once we gain confidence, we can remove the debug assert.