Make invoke arguments a struct

[namesty]

Currently, the invoke method takes in invocation arguments as separate function arguments. Making typical invocations look like:

client.invoke(uri, method, args, None, None)

One consideration brought up by @nerfZael is to make invocation arguments a struct, ideally something similar to:

struct InvokeArgs<T: Serialize> {
  uri: Uri,
  method: String,
  args: Option<T>,
  env: Option<&[u8]>,
  resolution_context: Option<&[u8]>
}

This would enable 2 main things:

• Having defaults:

client.invoke<R>(InvokeArgs { 
    uri: "test/hello",
    method: "sayHello",
    args: Some(MyArgs {...})
    ...Default::default()
}

• Passing method args as a serializable struct and encode it for the user; instead of forcing the user to encode them outside and pass them as an array of u8

The case for methods with no arguments would need to be handled