fix: trunc function with precision uses round instead of trunc semantics (#19794)

## Which issue does this PR close?

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- Closes #19793.

## Rationale for this change

The helper functions `compute_truncate32` and `compute_truncate64`
incorrectly use `.round()` instead of `.trunc()`, causing incorrect
results:
- `trunc(3.76, 1)` returned `3.8` (wrong - rounded)
- `trunc(3.76, 1)` should return `3.7` (correct - truncated)

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## What changes are included in this PR?

- Change `.round()` to `.trunc()` in `compute_truncate32` and
`compute_truncate64`
- Update unit test expected values to reflect correct truncation
behavior

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## Are these changes tested?

Yes. Unit tests updated and pass.

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## Are there any user-facing changes?

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Author: kumarUjjawal

datafusion/functions/src/math/trunc.rs

@@ -202,12 +202,12 @@ fn trunc(args: &[ArrayRef]) -> Result<ArrayRef> {
 
 fn compute_truncate32(x: f32, y: i64) -> f32 {
     let factor = 10.0_f32.powi(y as i32);
-    (x * factor).round() / factor
+    (x * factor).trunc() / factor
 }
 
 fn compute_truncate64(x: f64, y: i64) -> f64 {
     let factor = 10.0_f64.powi(y as i32);
-    (x * factor).round() / factor
+    (x * factor).trunc() / factor
 }
 
 #[cfg(test)]
@@ -238,9 +238,9 @@ mod test {
 
         assert_eq!(floats.len(), 5);
         assert_eq!(floats.value(0), 15.0);
-        assert_eq!(floats.value(1), 1_234.268);
+        assert_eq!(floats.value(1), 1_234.267);
         assert_eq!(floats.value(2), 1_233.12);
-        assert_eq!(floats.value(3), 3.312_98);
+        assert_eq!(floats.value(3), 3.312_97);
         assert_eq!(floats.value(4), -21.123_4);
     }
 
@@ -263,9 +263,9 @@ mod test {
 
         assert_eq!(floats.len(), 5);
         assert_eq!(floats.value(0), 5.0);
-        assert_eq!(floats.value(1), 234.268);
+        assert_eq!(floats.value(1), 234.267);
         assert_eq!(floats.value(2), 123.12);
-        assert_eq!(floats.value(3), 123.312_98);
+        assert_eq!(floats.value(3), 123.312_97);
         assert_eq!(floats.value(4), -321.123_1);
     }
 

datafusion/sqllogictest/test_files/scalar.slt

@@ -1165,7 +1165,7 @@ from small_floats;
 ----
 0.447 0.4 0.447
 0.707 0.7 0.707
-0.837 0.8 0.837
+0.836 0.8 0.836
 1 1 1
 
 ## bitwise and