bug: Simulation is not deterministic due to GenSignedMockTx

[adu-web3]

Summary of Bug

The simulation is not deterministic because we use a standalone random generator in GenSignedMockTx:

func GenSignedMockTx(gen client.TxConfig, msgs []sdk.Msg, feeAmt sdk.Coins, gas uint64, chainID string, accNums, accSeqs []uint64, priv ...cryptotypes.PrivKey) (sdk.Tx, error) {
	sigs := make([]signing.SignatureV2, len(priv))

	// create a random length memo
	r := rand.New(rand.NewSource(time.Now().UnixNano()))

	memo := simulation.RandStringOfLength(r, simulation.RandIntBetween(r, 0, 100))
...
}

This random generator use a different random seed from the simState.Rand, while GenSignedMockTx is widely used in x/{module}/operations.go to generate sdk.Tx.
This means even with the same random seed, the simulation could generate txs with different length of memo.
Therefore, ConsumeTxSizeGasMiddleware could consume different gas while executing the tx, which leads to non-deterministic appHash.

Version

master@450cd7fc8708ccb0fa21f05e251d9804a2063b79
release/v0.45.x

Steps to Reproduce

1. change `NumBlocks` to 1 in Makefile `test-sim-nondeterminism` section.
2. make test-sim-nondeterminism.
3. test failed.

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