interp: avoid useless interface wrapping

in `callBin`, call arguments are converted to the corresponding
parameter type. In a case of an interface, the original concrete type
should be preserved instead, and only wrapped to an interface type for
internal interpreter types, as runtime values should already implement the
interface.

This change removes the interface wrapping when parameter is a runtime
value (valueT or ptrT to valueT).

This removes some overhead when handling runtime values, and keep a
similar behavior between interpreted and pre-compiled code. For
example, `io.Copy` preserves its internal optimisations when passed a
`bytes.Buffer`.

interp/run.go

@@ -1187,6 +1187,7 @@ func callBin(n *node) {
 					c.val = reflect.Zero(argType)
 				}
 			}
+
 			switch c.typ.cat {
 			case funcT:
 				values = append(values, genFunctionWrapper(c))
@@ -1199,6 +1200,14 @@ func callBin(n *node) {
 				default:
 					values = append(values, genInterfaceWrapper(c, defType))
 				}
+			case ptrT:
+				if c.typ.val.cat == valueT {
+					values = append(values, genValue(c))
+				} else {
+					values = append(values, genInterfaceWrapper(c, defType))
+				}
+			case valueT:
+				values = append(values, genValue(c))
 			default:
 				values = append(values, genInterfaceWrapper(c, defType))
 			}