fix: correct cross join byte size statistics

[neilconway]

Which issue does this PR close?

• Closes stats_cartesian_product computes incorrect byte size for cross join #22699

Rationale for this change

stats_cartesian_product computes the total byte size of a cross join as:

      let total_byte_size = left_stats
          .total_byte_size
          .multiply(&right_stats.total_byte_size)
          .multiply(&Precision::Exact(2));

This is wrong (e.g., it multiplies two byte-size values together). The correct formula is "left-num-rows * right-size-in-bytes + right-num-rows * left-size-in-bytes", since the left side is repeated once per row on the right, and vice versa.

What changes are included in this PR?

• Fix total byte size formula for cross join
• Update expected SLT results

Are these changes tested?

Yes; covered by existing tests.

Are there any user-facing changes?

No.

[asolimando]

LGTM, indeed the updated formula is more accurate for cross join

[adriangb]

Thanks @neilconway