Enable propogation of fatal errors through io.Reader responses

**Is your feature request related to a problem? Please describe.**

A handler can gracefully force the process to be restarted by returning a `messages.InvokeResponse_Error` with `ShouldExit = true`. The usual way this happens is when the function `panic`s, but pass-through is allowed too on the handler's error value https://github.com/aws/aws-lambda-go/blob/caace586bdec3652223cc7761cc8c1c155a85601/lambda/errors.go#L20-L22

However, there's not an equivalent when the response value is a reader.

**Describe the solution you'd like**

Goal should be able to make this:
```go
type fatalReader struct{}
func (r *fatalReader) Read(_ []byte) (int, error) {
return 0, messages.InvokeResponse_Error{Type: "IDK", Message: "fatal", ShouldExit: true}
}
func handler() (any, error) {
return fatalReader{}, nil
}
```

result in the same logging and error reporting as this:
```go
func hander() (any, error) {
return nil, messages.InvokeResponse_Error{Type: "IDK", Message: "fatal", ShouldExit: true}
}
```

**Describe alternatives you've considered**

Might also expose something like https://github.com/aws/aws-lambda-go/blob/caace586bdec3652223cc7761cc8c1c155a85601/lambda/errors.go#L35-L46 in the public API, to make the construction of these fatal errors easier.