Latest finalized block cache

[maxconway]

This introduces caching of the latest finalized block.

Not ready for merging - I want to talk over how we test performance first

[github-actions]

Bencher Report

Branch	max/db_cache
Testbed	self-hosted

Click to view all benchmark results

Benchmark	Latency	Benchmark Result milliseconds (ms) (Result Δ%)	Upper Boundary milliseconds (ms) (Limit %)
full-blocks-erc20-transfers/full-blocks-erc20-transfers	📈 view plot 🚷 view threshold	764.12 ms (-72.77%) Baseline: 2,806.17 ms	6,404.42 ms (11.93%)
full-blocks-evm-transfers/full-blocks-evm-transfers	📈 view plot 🚷 view threshold	1,049.20 ms (-67.70%) Baseline: 3,248.59 ms	8,660.44 ms (12.11%)
full-blocks-giant-deploy/full-blocks-giant-deploy	📈 view plot 🚷 view threshold	6,166.60 ms (-14.41%) Baseline: 7,204.41 ms	9,745.15 ms (63.28%)
full-blocks-scilla-add/full-blocks-scilla-add	📈 view plot 🚷 view threshold	1,167.60 ms (-10.99%) Baseline: 1,311.69 ms	1,741.12 ms (67.06%)
full-blocks-scilla-load/full-blocks-scilla-load	📈 view plot 🚷 view threshold	3,914.00 ms (-10.21%) Baseline: 4,358.87 ms	5,500.71 ms (71.15%)
full-blocks-scilla-store/full-blocks-scilla-store	📈 view plot 🚷 view threshold	3,312.90 ms (-9.30%) Baseline: 3,652.71 ms	4,493.60 ms (73.72%)
full-blocks-zil-transfers/full-blocks-zil-transfers	📈 view plot 🚷 view threshold	1,326.60 ms (-57.39%) Baseline: 3,113.32 ms	5,886.94 ms (22.53%)
process-empty/process-empty	📈 view plot 🚷 view threshold	10.26 ms (-16.27%) Baseline: 12.26 ms	14.21 ms (72.22%)

🐰 View full continuous benchmarking report in Bencher