test: Add regression test for limit / sort

[alamb]

Which issue does this PR close?

• Follow on to fix: Avoid pushing down sort under limits #25408

Rationale for this change

@jayzhan211 suggests

• fix: Avoid pushing down sort under limits #25408 (comment)

This PR also fixes a wrong-result bug on main: with multiple partitions, an OFFSET-only subquery over ORDER BY b followed by ORDER BY b, a returns 1, 21, 4, 24, … on main, because the [b, a] sort is pushed under SortPreservingMergeExec: [b]. Please add a result check so this doesn't regress:

statement ok
set datafusion.execution.target_partitions = 4;

statement ok
CREATE TABLE src (a INT, b INT) AS VALUES (1, 3), (2, 1), (3, 2), (4, 3), (5, 1), (6, 2), (7, 3), (8, 1);

statement ok
CREATE TABLE t AS SELECT a, b FROM src UNION ALL SELECT a + 10, b FROM src
  UNION ALL SELECT a + 20, b FROM src UNION ALL SELECT a + 30, b FROM src;

query II
SELECT * FROM (SELECT a, b FROM t ORDER BY b OFFSET 20) ORDER BY b, a;
----
1 3
4 3
7 3
11 3
14 3
17 3
21 3
24 3
27 3
31 3
34 3
37 3

What changes are included in this PR?

Add this test

What is the testing strategy for this PR?

Are there any user-facing changes?

Only tests

[alamb]

note this test fails on main