Cql::Uuid#eql? fails when a non-UUID is compared

Currently if you attempt to compare a Cql::Uuid with most other classes, it will fail with the following:

```
NoMethodError: undefined method `value' for ...
```

This is because the `eql?` method blindly calls `#value` on the object being compared.

This PR fixes the issue by returning false if the object being compared is not a Cql::Uuid or descendant.