feat: fuzzing

[gakonst]

Closes #16

Introduces fuzzing of solidity test functions with >0 arguments, using the proptest library.

This is done in 2 parts:

1. Defining the fuzzing rules in fuzz.rs which basically says "take in an ABI type and generate a fuzzing strategy for it" and then "combine all fuzzing strategies for a certain function to a strategy for fuzzing the function's calldata"
2. Changing runner.rs to execute proptest's TestRunner if >0 inputs are detected for the current function.

A requirement of fuzzing was to make the EVM cloneable, since the TestRunner only accepts Fns which cannot mutate their environment, meaning that we had to add a Clone restriction on it in the fuzzing-related code.

(To facilitate that, we need rust-ethereum/evm#61 for Sputnik and vorot93/evmodin#9 for EvmOdin)

TODO:

• Expand the types being fuzzed.
• See if we can remove the Clone requirement by using a factory, and splitting the fuzz tests to a separate function so we can run fuzz tests w/o tracing even when the EVM uses a tracer in non-fuzz tests