Repository: pykeen/pykeen
Issue: Unexpected behaviour when using split() on a TriplesNumericLiteralsFactory object.
Root cause: Algorithmic Error

**Describe the bug**

When using the `TriplesNumericLiteralsFactory` split() function, the returned objects are `TriplesFactory` objects, which i think should not be the expected behavior since the literal information is lost in the process.

**To Reproduce**

``` python
import numpy as np
from pykeen.triples import TriplesNumericLiteralsFactory

TRIPLES = np.array(
    [
        ['peter', 'likes', 'chocolate_cake'],
        ['chocolate_cake', 'isA', 'dish'],
        ['susan', 'likes', 'chocolate_cake'],
        ['susan', 'likes', 'pizza'],
        ['peter', 'likes', 'susan'],
        ['peter', 'likes', 'mango'],
        ['mango', 'isA', 'fruit'],
        ['peter', 'isA', 'person'],
        ['susan', 'isA', 'person'],
    ],
    dtype=str,
)

NUMERIC_TRIPLES = np.array(
    [
        ['peter', '/lit/hasAge', '30'],
        ['peter', '/lit/hasHeight', '185'],
        ['peter', '/lit/hasChildren', '2'],
        ['susan', '/lit/hasAge', '28'],
        ['susan', '/lit/hasHeight', '170'],
    ],
    dtype=str,
)


tf = TriplesNumericLiteralsFactory(triples=TRIPLES, numeric_triples=NUMERIC_TRIPLES)
training, testing = tf.split()
print(training)
print(testing)
```
Current output:
```
using automatically assigned random_state=640982782
TriplesFactory(num_entities=8, num_relations=2, num_triples=7, inverse_triples=False)
TriplesFactory(num_entities=8, num_relations=2, num_triples=2, inverse_triples=False)
```

**Expected behavior**
The expected behavior would be that the use of the split function on a `TriplesNumericLiteralsFactory` it should return 2 (or more depending on the split arguments) `TriplesNumericLiteralsFactory` objects instead of `TriplesFactory` objects.

Example of expected output to previous example:
```
using automatically assigned random_state=640982782
TriplesNumericLiteralsFactory(num_entities=8, num_relations=2, num_triples=7, inverse_triples=Falsenum_literals=3)
TriplesNumericLiteralsFactory(num_entities=8, num_relations=2, num_triples=2, inverse_triples=Falsenum_literals=3)
```

**Environment:**

| Key             | Value                    |
|-----------------|--------------------------|
| OS              | posix                    |
| Platform        | Linux                    |
| Release         | 5.4.104+                 |
| Time            | Thu Sep 23 09:10:01 2021 |
| Python          | 3.7.12                   |
| PyKEEN          | 1.5.1-dev                |
| PyKEEN Hash     | UNHASHED                 |
| PyKEEN Branch   |                          |
| PyTorch         | 1.9.0+cu102              |
| CUDA Available? | true                     |
| CUDA Version    | 10.2                     |
| cuDNN Version   | 7605                     |


I have an easy fix (not sure if the most efficient) for the problem, if you think its relevant I can open a PR.

> I have an easy fix (not sure if the most efficient) for the problem, if you think its relevant I can open a PR.

Hi @Rodrigo-A-Pereira , your PR would be highly welcome!

Closed by #594