Add `CAST` to `parser.py`

### Feature Request / Improvement

I think I have somewhat of an idea on how to do this, so far have added the following to `parser.py`:

```py
CAST = CaselessKeyword("cast")
cast_expression = (CAST + "(" + column + "as" + identifier + Suppress(")")).set_results_name("cast")

# would need something special for the set_parse_action
```

I am wondering a couple of things:
Do we need a new class `CastableReference` or something? Worth expanding on the `Reference` class? And once that is done, how would we propagate the new type (Im assuming we need some way to go from a string to an `IcebergType` of the string the user has put into the cast operation) into the scan?

This was spawned from https://github.com/apache/iceberg-python/issues/170

Happy to work on this, just would be awesome to get some context

Comece com parser.py e o contexto da issue 170. Rastreie a classe Reference existente e as ações de parsing; em seguida, acompanhe como as expressões analisadas chegam ao scan e como as strings se tornam valores de IcebergType. Está concluído quando a sintaxe CAST for analisada e seu tipo de destino for propagado para o scan.

Escrita pelo modelo de indexação a partir do texto da issue.