[Python] Explode multiple columns with different lengths

I have a dataframe like:

data = {
"a": [[1], [2], [3, 4], [5, 6, 7]],
"b": [[], [8], [9, 10], [11, 12]],
}
df = pl.DataFrame(data)
"""
┌───────────┬───────────┐
│ a ┆ b │
│ --- ┆ --- │
│ list[i64] ┆ list[i64] │
╞═══════════╪═══════════╡
│ [1] ┆ [] │
│ [2] ┆ [8] │
│ [3, 4] ┆ [9, 10] │
│ [5, 6, 7] ┆ [11, 12] │
└───────────┴───────────┘
"""


Each pair of lists may not have the same length, and I want to "truncate" the explode to the shortest of both lists:

"""
┌─────┬─────┐
│ a ┆ b │
│ --- ┆ --- │
│ i64 ┆ i64 │
╞═════╪═════╡
│ 2 ┆ 8 │
│ 3 ┆ 9 │
│ 4 ┆ 10 │
│ 5 ┆ 11 │
│ 6 ┆ 12 │
└─────┴─────┘
"""


I was thinking that maybe I'd have to fill the shortest of both lists with None to match both lengths, and then drop_nulls. But I was wondering if there was a more direct approach to this?

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