Handle MAX_INT_256 and malicious ER20 sends

[zmanian]

1. We need a pull request on the Cosmos SDK upstream to increase the maxBitLength of SDK.Int to 257 bits to ensure and a test the check the SDK.Int can deserialize the max ERC20 value.

`_, err := sdk.NewIntFromString("115792089237316195423570985008687907853269984665640564039457584007913129639935")`

should be in the test case.

We need a check in

func (a EthereumEventProcessor) Handle to ensure that adding the amount send to Cosmos doesn't overflow the max size of SDK.Int.

If it does overflow we should increment the event nonce but ignore the amount sent.

[jtremback]

If it does overflow we should increment the event nonce but ignore the amount sent.

I think it already does work this way, as a natural outcome of ctx.CacheContext on https://github.com/PeggyJV/gravity-bridge/blob/main/module/x/gravity/keeper/ethereum_event_vote.go#L120

[albertchon]

cosmos/cosmos-sdk#9511 closes this issue

[zmanian]

I don't see anything in ctx.CacheContext that will catch a panic. I think this only handles an error and not a panic.

[zmanian]

We need a panic handler here. Not just an error handler.

[albertchon]

FYI we fixed this in our fork without a panic handler