feat: precompilegen Solidity interface -> stateful precompile

[ARR4N]

Why this should be merged

Note that this is not a full replacement for ava-labs/subnet-evm/cmd/precompilegen. The original conflates the general concept of stateful precompiles with Ava-specific functionality (e.g. implementation configuration, module registration, etc.) while this is purely a mechanism for creating precompiles that conform to Solidity interfaces. In addition to the benefits I outline below, there is a case for separation of concerns.

The primary benefit of this approach is that the implementation is separate from the wrapper that converts it into a vm.PrecompiledContract. The subnet-evm generator leaves place for custom code to be inserted, making it impossible to update the boilerplate without overwriting customisation.

How this works

Code generation is analogous to gRPC server stubs:

	gRPC	precompilegen
Input	proto	Solidity -> solc ABI output
Generated	type FooServer interface	type Contract interface
Construction	func RegisterFooServer(..., FooServer)	func New(Contract) vm.PrecompiledContract

interface IPrecompile {
    function Foo(uint256) external returns (bool);
}

becomes

type Contract interface {
    Fallback(vm.PrecompileEnvironment, []byte) ([]byte, error)
    Foo(vm.PrecompileEnvironment, *big.Int) (bool, error)
}

func New(Contract) vm.PrecompiledContract { ... }

which is used for the return values of params.RulesHooks.PrecompileOverride.

Tip

See libevm/precompilegen/testprecompile/generated.go for output and libevm/precompilegen/gen_test.go for usage.

To-do

• Remove explicit gas return argument in favour of contract.UseGas() bool equivalent on vm.PrecompileEnvironment (refactor: PrecompileEnvironment.{,Use,Refund}Gas() in lieu of args #73).
• Explore payable and view/pure implications.

How this was tested

Integration test exercising Solidity-based test via a simulated.Backend.