transform_chart breaks with BinParams extent

```
from altair_transform import transform_chart
transform_chart(
alt.Chart(cdf2.select(pr.col("cleaned_stat_len")).to_pandas().head(100))
.mark_bar()
.encode(
x=alt.X("binned_len:O"),
y=alt.Y("count()", scale=alt.Scale(type="log")),
tooltip="count()",
).transform_bin(
'binned_len', field='cleaned_stat_len', bin=alt.Bin(maxbins=50, extent=[0, 100])
)
)

Truncated Traceback (Use C-c C-$ to view full TB):
File ~/dev/instant-science/trademark/.venv/lib/python3.9/site-packages/altair_transform/transform/bin.py:36, in visit_bin(transform, df)
33 field = transform_dct["field"]
34 extent = df[field].min(), df[field].max()
---> 36 bins = calculate_bins(extent, **({} if bin is True else bin))
38 if isinstance(col, str):
39 df[col] = _cut(df[field], bins, return_upper=False)

TypeError: calculate_bins() got multiple values for argument 'extent'
```