dolt_diff_stat emits an all-zero row for an in-place column rename where Dolt emits none

Cosmetic parity nit, likely low priority — an all-zero row and no row arguably say the same thing. Filing mainly to record the characterization, and the trap in the obvious fix.

Pre-existing on master. Found while doing #1998.

## Repro

```sql
CREATE TABLE t(id INT PRIMARY KEY, v INT);
INSERT INTO t VALUES(1,10),(2,20);
SELECT dolt_commit('-Am','seed');
ALTER TABLE t RENAME COLUMN v TO w;
SELECT dolt_commit('-Am','c2');
SELECT * FROM dolt_diff_stat('HEAD~1','HEAD');
```

doltlite returns one row, everything zero including the row counts:

```
t ru=0 ra=0 rd=0 rm=0 ca=0 cd=0 cm=0 orc=0 nrc=0
```

Dolt 2.2.2 returns no rows. Same on an empty table, and for `ALTER TABLE t MODIFY COLUMN v VARCHAR(50)`.

## Do not "fix" it by narrowing the emission gate

The tempting change is to drop the `schemaChanged` exception in `dstAdvance` (`src/doltlite_diff_stat.c`), so a table with no counters gets no row. I tried it. It makes this case pass and **breaks `diff_stat_revert_schema_change_with_later_added_table`** in `test/vc_oracle_diff_stat_test.sh`, where Dolt *does* emit an all-zero row.

What Dolt actually does, as far as I probed:

| schema-only change, no data change | Dolt |
|---|---|
| `ALTER TABLE t RENAME COLUMN v TO w` | no row |
| `ALTER TABLE t MODIFY COLUMN v VARCHAR(50)` | no row |
| recreate with a CHECK, `DROP TABLE t`, `RENAME TO t` | all-zero row |

So the row appears when the table was *recreated*, not when its columns changed in place. Matching that needs table-identity reasoning rather than a counter test, which is why #1998 left it alone.

`rename_column_no_data_change` in `test/vc_oracle_diff_stat_test.sh` currently runs summary-only for this reason, with a comment pointing at the trap. If this is closed as wontfix, that case can stay as it is.

Start in src/doltlite_diff_stat.c, especially dstAdvance, and read rename_column_no_data_change and diff_stat_revert_schema_change_with_later_added_table in test/vc_oracle_diff_stat_test.sh. Run the supplied SQL reproduction and these tests first. Done means matching Dolt for in-place schema changes without breaking the all-zero row for recreated tables.

Written by the indexing model from the issue text.