Add accounting enforcement on Deposits

[NiloCK]

Currently, users can print ETH on monomer supported appchains by specifying an L2 mint value greater than the value they supply to the L1 portal contract.

Probably that shouldn't work.

PoC here with a one-eth L1 tx and a 5 eth L2 mint. The test passes and the mint_eth event fires with value 5 eth.