Deposit contract gas reduction

[86667]

This PR contains two options for mitigating the issue described in #1991.

Solution 1

The first solution found in file deposit_v4 is a general reduction in the gas used across the contract. These changes reduce the reading and writing to storage when writing future committees but the issue of uneven gas costs remains.

The effects of the changes can be seen in the below table:

Call	Before	After
Deposit owner1	348311	346633
Deposit owner2	584151	585667
depositTopUp owner1	337149	258079
depositTopUp owner2	13484	13484
2nd depositTopUp owner1	202925	34310
2nd depositTopUp owner2	13499	13499

The 2nd depositTopUp is so much cheaper because we do not need to write new keys to storage, only update the balances.

Solution 2

The second solution is in deposit_v5. This is an attempt to remove the uneven gas cost of the depositTopUp() call by removing the need to write futureCommittee all together and having the committee calculated on the fly whenever it is required.

The code's outline is complete but the solution is unfinished. TODO:

• Run gas usage tests to understand how the cost of calculating committee() scales with number of depositors. Is it acceptable to pay this gas fee in all scenarios in which it is called?
• The solution removed the need for StakerMoved. Figure out how we can continue to support the behavior expected by third parties and consensus

[github-actions]

Bencher Report

Branch	deposit_v3_gas_reduction
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	1,745.90 (+27.55%)	1,848.51 (94.45%)
full-blocks-evm-transfers/full-blocks-evm-transfers	📈 view plot 🚷 view threshold	455.73 (-23.50%)	740.13 (61.57%)
full-blocks-zil-transfers/full-blocks-zil-transfers	📈 view plot 🚷 view threshold	4,899.90 (+16.58%)	5,385.33 (90.99%)
process-empty/process-empty	📈 view plot 🚷 view threshold	7.59 (-15.37%)	10.50 (72.25%)

🐰 View full continuous benchmarking report in Bencher