Join per-column stats not scaled with estimated row count

[neilconway]

Describe the bug

For inner/left/right/full joins, estimate_join_cardinality concatenates both inputs' column statistics verbatim and never adjusts them to the estimated output cardinality:

• Count-like fields (null_count, distinct_count, byte_size, sum_value) aren't scaled to the join's fan-out/selectivity, so they can be inconsistent with the output num_rows.
• Outer joins don't NULL-pad the non-preserved side, even though the side-to-pad is already known (utils.rs:240-242).
• Equi-join key columns aren't intersected (min/max) or NDV-bounded (min(left_ndv, right_ndv)).

Related to #22743 but the general join case might be a bit more involved.

To Reproduce

No response

Expected behavior

No response

Additional context

No response

[neilconway]

take