[Python] Casting expression result

Would it be possible to cast an expression into a specific datatype without casting the source columns?

Consider the following frame:

df = pl.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]}, schema={'A': pl.UInt8, 'B': pl.UInt8})

┌─────┬─────┐
│ A ┆ B │
│ --- ┆ --- │
│ u8 ┆ u8 │
╞═════╪═════╡
│ 1 ┆ 4 │
│ 2 ┆ 5 │
│ 3 ┆ 6 │
└─────┴─────┘


Now using an expression:

df = df.with_columns((pl.col("A") - pl.col("B")).alias("C"))

┌─────┬─────┬─────┐
│ A ┆ B ┆ C │
│ --- ┆ --- ┆ --- │
│ u8 ┆ u8 ┆ u8 │
╞═════╪═════╪═════╡
│ 1 ┆ 4 ┆ 253 │
│ 2 ┆ 5 ┆ 253 │
│ 3 ┆ 6 ┆ 253 │
└─────┴─────┴─────┘


This is obviously correct in comp-sci terms but not practical. Can I only resolve this by first casting "A" and "B" to a signed integer or is there a better/more concise way?

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