fix: respect volatility for all function expressions

[1fanwang]

Which issue does this PR close?

Closes #25504.

Rationale for this change

Repeated calls to a volatile higher-order UDF can reuse the first call's result. Comparing two calls can also return true without invoking the function. Both queries now execute each call.

What changes are included in this PR?

The volatility check reads the declared signature for aggregate, window and higher-order expressions, as it already does for scalar expressions. This includes aggregates used as window functions. The join optimizer uses the shared repeatability check instead of checking aggregate volatility separately.

What is the testing strategy for this PR?

The regression registers a counter UDF and runs both queries through the SQL engine. It also checks every function kind, volatility level and aliased expression. Join-optimizer controls preserve DISTINCT handling and reject volatile expressions and subqueries.

On macOS arm64 with Rust 1.98.1 and the pinned test data:

cargo test --locked --profile ci -j6 -p datafusion --test user_defined_integration volatility -- --nocapture
cargo test --locked --profile ci -j6 -p datafusion-expr -p datafusion-optimizer --lib
cargo test --locked --profile ci -j6 -p datafusion-sqllogictest --test sqllogictests -- --test-threads 6 cse.slt expr.slt array_transform.slt eliminate_outer_join.slt aggregates_simplify.slt

Raw logs

Before the fix:

+-------+--------+
| first | second |
+-------+--------+
| 0     | 0      |
+-------+--------+
calls=1
+-------+
| equal |
+-------+
| true  |
+-------+
calls=0

After:

+-------+--------+
| first | second |
+-------+--------+
| 0     | 1      |
+-------+--------+
calls=2
+-------+
| equal |
+-------+
| false |
+-------+
calls=2
Progress: 6/6 files completed (100%)
slt_exit_code=0

Are there any user-facing changes?

The affected queries return the results of separate function calls. There is no public API change.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.50%. Comparing base (e2ca7f3) to head (813d657).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25511      +/-   ##
==========================================
- Coverage   82.50%   82.50%   -0.01%     
==========================================
  Files        1140     1140              
  Lines      438050   438057       +7     
  Branches   438050   438057       +7     
==========================================
+ Hits       361415   361417       +2     
  Misses      54829    54829              
- Partials    21806    21811       +5     

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[neilconway]

There's also #25513 for the same bug

[1fanwang]

#25513 is closed without merging. This PR includes SQL regressions for projection reuse and equality simplification.

[neilconway]

Overall looks reasonable!

Can we cleanup/simplify is_duplicate_insensitive_aggregate, please?

[1fanwang]

Done in 97efd3a.

[neilconway]

Thanks @1fanwang !