refactor!: gas consumption for stateful precompiles

[ARR4N]

Why this should be merged

Support simultaneous running of a stateful precompile and computation of its gas consumption.

Closes #17. Re the Caution in said issue, the 63/64 rule is already handled by geth.

How this works

The requiredGas func(...) argument of NewStatefulPrecompile() is removed. In its place, the function signature of a stateful precompile accepts supplied gas and returns gas remaining; this was renamed from PrecompiledStatefulRun to PrecompiledStatefulContract as it's no longer just the execution.

type PrecompiledStatefulContract func(env PrecompileEnvironment, input []byte, suppliedGas uint64) (ret []byte, remainingGas uint64, err error)

How this was tested

Existing unit tests for stateful precompiles, refactored accordingly.