test: consolidate ASOF SQL coverage

[Xuanwo]

Which issue does this PR close?

• Part of ASOF join support / Specialize Range Joins #318.
• Follow-up to feat: support ASOF JOIN SQL #23830.

Rationale for this change

ASOF SQL behavior was split between sqllogictest and Rust integration tests. SQL-visible results and plan shapes are easier to review and maintain in SLT, while Rust coverage remains useful for execution setup that SLT cannot express.

What changes are included in this PR?

• Move duplicated coercion, EXPLAIN, USING output, and validation coverage into asof_join.slt.
• Add result and plan-shape coverage for right-output filtering, projection pruning, expression operands, empty inputs, duplicate left rows, self joins, and multi-key USING.
• Keep Rust tests that require multi-partition physical plans, unbounded inputs, cross-batch execution, or direct plan-to-SQL roundtrips.

Are these changes tested?

Yes:

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --profile ci -p datafusion-sqllogictest --test sqllogictests -- asof_join
• cargo test --profile ci -p datafusion --test core_integration --all-features -- asof
• Extended workspace tests from the contributor guide

Are there any user-facing changes?

No. This consolidates and expands coverage for the existing ASOF SQL contract.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.69%. Comparing base (c0e872f) to head (702f8c0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24964      +/-   ##
==========================================
- Coverage   82.69%   82.69%   -0.01%     
==========================================
  Files        1147     1147              
  Lines      447348   447348              
  Branches   447348   447348              
==========================================
- Hits       369936   369927       -9     
- Misses      54999    55006       +7     
- Partials    22413    22415       +2     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Xuanwo]

Hi @jayzhan211 and @2010YOUY01, this ASOF test coverage follow-up is now restacked and ready for review. Would you mind taking a look when you have time? Thanks!

[jayzhan211]

This test only passes because l sorts before r. exclude_using_columns keeps the USING key whose qualifier sorts first. With x/a aliases, SELECT * emits a.grp, which is NULL for unmatched left rows and lands in column 3, while SELECT grp still returns x.grp. The deleted Rust assertion (t/p → ["ts", "trade_id", "symbol", ...]) was the only test for that case, so please keep it here:

-# SELECT * exposes the USING key once.
+# SELECT * exposes the USING key once, keeping the key whose qualifier sorts
+# first (`l` < `r` keeps the left key).

# With the right alias sorting first, SELECT * keeps the right key, which is
# NULL for unmatched left rows.
query IPTPT
SELECT *
FROM asof_left x
ASOF JOIN asof_right a
MATCH_CONDITION (x.ts >= a.ts)
USING (grp)
WHERE x.id IN (1, 2)
ORDER BY x.id;
----
1 2024-01-01T09:00:01 NULL NULL NULL
2 2024-01-01T09:00:04 A 2024-01-01T09:00:04 a4

[Xuanwo]

@jayzhan211 nice catch! Will fix.

[jayzhan211]

Thanks @Xuanwo !