[WIP] Refactor sync out of block_store.rs

[shawn-zil]

This PR attempts to take the block syncing feature out of block_store.rs.

It performs syncing using a 3-phase mechanism:

1. Build an in-memory chain history.
2. Fetches the proposals for this chain history and injects them into the pipeline.
3. Injects the latest proposals into the pipeline.

It is working on the local docker cluster - a new node is able to sync from genesis, and sync from elsewhere in history.

TODOs include:

1. more checks;
2. removal of the (now unused) portion from block_store.rs.

[github-actions]

Bencher Report

Branch	2039-refactor-blockstore
Testbed	self-hosted

Click to view all benchmark results

Benchmark	Latency	Benchmark Result milliseconds (ms) (Result Δ%)	Upper Boundary milliseconds (ms) (Limit %)
process-empty/process-empty	📈 view plot 🚷 view threshold	8.40 (-8.17%)	10.35 (81.23%)
produce-full/produce-full	📈 view plot 🚷 view threshold	1,725.90 (-12.36%)	2,315.19 (74.55%)

🐰 View full continuous benchmarking report in Bencher