Parquet statistics are collected twice

Currently, the parquet reader is using `split_row_groups='infer'` to infer whether it should split a file into multiple dask tasks or not which is done by collecting parquet statistics from every file.

Running the code below triggers this statistics collection twice. Once during the definition of the computation / while I'm mutating the dataframe and once as soon as I call compute.

```python
import dask_expr as dd

VAR1 = datetime(1998, 9, 2)

lineitem_ds = dd.read_parquet("s3://coiled-runtime-ci/tpc-h/scale-1000/lineitem")

lineitem_filtered = lineitem_ds[lineitem_ds.l_shipdate <= VAR1]
lineitem_filtered["sum_qty"] = lineitem_filtered.l_quantity
lineitem_filtered["sum_base_price"] = lineitem_filtered.l_extendedprice
lineitem_filtered["avg_qty"] = lineitem_filtered.l_quantity
lineitem_filtered["avg_price"] = lineitem_filtered.l_extendedprice

# This line now triggers a statistics collection iff `split_row_groups` is not False
lineitem_filtered["sum_disc_price"] = lineitem_filtered.l_extendedprice * (
1 - lineitem_filtered.l_discount
)

lineitem_filtered["sum_charge"] = (
lineitem_filtered.l_extendedprice
* (1 - lineitem_filtered.l_discount)
* (1 + lineitem_filtered.l_tax)
)

lineitem_filtered["avg_disc"] = lineitem_filtered.l_discount
lineitem_filtered["count_order"] = lineitem_filtered.l_discount

gb = lineitem_filtered.groupby(["l_returnflag", "l_linestatus"])

total = gb.agg(
{
"sum_qty": "sum",
"sum_base_price": "sum",
"sum_disc_price": "sum",
"sum_charge": "sum",
"avg_qty": "mean",
"avg_price": "mean",
"avg_disc": "mean",
"count_order": "count",
}
)

# Once I compute, another stats collection is triggered
total.compute()
```


related to https://github.com/dask-contrib/dask-expr/issues/363

Start by running the supplied dask_expr example and tracing the parquet reader's split_row_groups='infer' path during dataframe mutation and compute. Identify why statistics are collected in both phases; done when the same computation collects parquet statistics only once while preserving task-splitting behavior.

Written by the indexing model from the issue text.