feat: deposit_v4 with cheaper depositTopUp

[86667]

Reduce the work done by updateLatestComputedEpoch() to minimise gas cost of depositTopUp().

To view diff with deposit_v3 eg:

diff ~/zq2/zilliqa/src/contracts/deposit_v3.sol ~/delegated_staking/test/deposit-development/deposit_v4.sol 

Results

Gas costs before:

1st top up owner 1: Gas used 341943
1st top up owner 2: Gas used 16149

Rolling ahead 1 epoch
2nd top up owner 1: Gas used 111502
2nd top up owner 2: Gas used 16149

Rolling ahead a 2 epochs
3rd top up owner 1: Gas used 205615
3rd top up owner 2: Gas used 16158

After:

1st top up owner 1: Gas used 262857
1st top up owner 2: Gas used 16149

Rolling ahead 1 epoch
2nd top up owner 1: Gas used 27168
2nd top up owner 2: Gas used 16149

Rolling ahead a 2 epochs
3rd top up owner 1: Gas used 36947
3rd top up owner 2: Gas used 16158

Showing that it costs ~120_000 gas per new key added and is charged to whoever is first to call deposit(), unstake() or depositTopUp() AFTER a deposit is made and one epoch has passed. If 2 or more epochs pass and none of those fns are called, then the next to call them must pay to write the new key into 2 committees, meaning a cost of ~240_000 gas.

Outstanding TODO

First TopUp pays for writing of stakerKeys for inititial deposits.

[86667]

Moved changes to zq2 repo - Zilliqa/zq2#2102