Transaction Simulator

Runs the call through eth_call and estimateGas together, because either can fail while the other succeeds — a reverting call still tells you why, and a succeeding call may still fail to estimate. Decodes the return value against an ABI if you supply one. Probes first whether the RPC supports state overrides, and if it does not, says so plainly: simulation still works against real state, you just cannot pretend to hold tokens you do not have. State override support is probed first and reported honestly. Without it, simulation runs against real current state, which still answers whether a call reverts and what it costs — you simply cannot pretend to hold tokens you do not have. Nothing is ever sent; this only ever reads.