feat: support Groth16 for wrapper circuit

[mattstam]

Using the CLI, you can now choose between Groth16 and Plonk via the --system flag:

succinctx/plonky2x/verifier/cli.go

Line 38 in ec30e7c

if *systemFlag == "groth16" {

where each proving system implements this interface:

type ProvingSystem interface {
	Compile() error
	Prove() error
	Verify() error
	Export() error
}