Improve error message for invalid input

Right now, the error message passing an invalid object to `array_namespace` is 
```
The input is not a supported array type
```
It would be more useful for debugging to say which class failed, I think. E.g.:
```
"generator" is not a supported array type
```
```
"map" is not a supported array type
```
```
"float" is not a supported array type
```
