Support simulations

[larry0x]

Currently the Ante/PostHandler don't support simulations, meaning we can't estimate gas if a tx is initiated by an AbstractAccount. We should implement proper simulation.

NOTE: we have to register relevant types in legacy amino codec, because a certain sdk AnteHandler involved in the simulation still uses amino: https://github.com/cosmos/cosmos-sdk/blob/v0.47.2/x/auth/ante/basic.go#L124-L130

Additionally, we need a custom authcmd.GetSimulationCmd method (see: cosmos/cosmos-sdk#16887)

[larry0x]

A few possible designs to the sudo API:

Design 1

Introduce two new methods: BeforeTxSim and AfterTxSim

enum SudoMsg {
    BeforeTx {
        msgs: Vec<Any>,
        tx_bytes: Binary,
        credential: Binary,
    },
    BeforeTxSim {
        msgs: Vec<Any>,
        tx_bytes: Binary,
        // the credential isn't provided in simulation mode
    },
    AfterTx {},
    AfterTxSim {},
}

Design 2

Make credential optional (None in simulation mode), and add a new simulation field indicating whether it's simulation mode:

enum SudoMsg {
    BeforeTx {
        msgs: Vec<Any>,
        tx_bytes: Binary,
        // None if the tx is being run in the simulation mode
        credential: Option<Binary>,
        // whether the tx is being run in the simulation mode
        simulation: bool,
    },
    AfterTx {
        simulation: bool,
    },
}

Design 3

Define a new Credential type as follows:

enum Credential {
    Bytes(Binary),
    Simulation,
}

enum SudoMsg {
    BeforeTx {
        msgs: Vec<Any>,
        tx_bytes: Binary,
        credential: Credential,
    },
    AfterTx {
        simulation: bool,
    },
}

[larry0x]

going with option 2

option 2 seems the best considering that we can allow the credential to be None even if not in simulation mode:

larry_0x, [8 Jul 2023 at 01:14:58]:
we can imagine uses cases where an account may not need a credential. for example, an account that anyone can use to send a tx, but only once an hour. something like this
some interesting game mechanics can perhaps be built this way