Add `cast` function for creating logical cast expression

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
When using the dataframe API there is no easy way to cast a column to another type

Describe the solution you'd like
I would like a cast function something like this:

fn cast(expr: Expr, data_type: DataType) -> Expr {
    Expr::Cast {
        expr: Box::new(expr),
        data_type,
    }
}

This would allow me to then write dataframe code like this:

.with_column(
    "unixReviewTimestamp",
    cast(
        col("unixReviewTime"),
        DataType::Timestamp(TimeUnit::Millisecond, None),
    ),
)?

Describe alternatives you've considered
None

Additional context
None

[turbo1912]

I can pick this up if no one is working on it