Unmarshalling to an interface type?

It this supported? For example:

```go
// Package main implements a test JSON-RPC cli client
package main

import (
"context"
"flag"
"fmt"
"net"
"net/http"

"github.com/filecoin-project/go-jsonrpc"
"go.mills.io/saltyim"
)

func main() {
flag.Parse()

httpc := &http.Client{
Transport: &http.Transport{
DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {
return net.Dial("unix", flag.Arg(0))
},
},
}

var cli struct {
Me func() saltyim.Addr
String func() string
}

closer, err := jsonrpc.NewMergeClient(
context.Background(),
"http://example.com",
"Client",
[]any{&cli},
nil,
jsonrpc.WithHTTPClient(httpc),
)
if err != nil {
panic(err)
}
defer closer()

fmt.Printf("String():\n%s\n", cli.String())

me := cli.Me()
fmt.Printf("Me(): #%v\n", me)
}
```

Currently I get `nil` for a call to `cli.me()` 🤔