Figure out problem with Cosmos Txs replacement

this test: [https://github.com/cosmos/evm/blob/ae62ea201431d0d9148cb27d56ff8d6c6edc59c9/tests/systemtests/mempool/test_replacement.go#L137](https://github.com/cosmos/evm/blob/ae62ea201431d0d9148cb27d56ff8d6c6edc59c9/tests/systemtests/mempool/test_replacement.go#L137)

is disabled. currently cosmos tx replacement is not supported.

Start with tests/systemtests/mempool/test_replacement.go at line 137 and inspect why the test is disabled. Review the surrounding replacement-test behavior and the issue's statement that Cosmos transaction replacement is unsupported. Done means the relevant replacement test is enabled and passes once transaction replacement support is implemented.

Written by the indexing model from the issue text.