fix(literals): Return Long bounds for Decimal conversion (#3470)

Closes #3469

# Rationale for this change

Decimal literals converted to `LongType` should use long bound sentinels
when the value is outside the long range. The existing conversion
returned integer sentinels, mismatching the requested target type.

This returns `LongAboveMax` and `LongBelowMin` for decimal-to-long
overflow.

### Relationship to Java

Java's `DecimalLiteral.to(...)` only handles `DECIMAL` and returns
`null` for other target types
([`Literals.java#L497-L505`](https://github.com/apache/iceberg/blob/main/api/src/main/java/org/apache/iceberg/expressions/Literals.java#L497-L505)),
so there is no direct decimal-to-long branch to mirror. This keeps
PyIceberg's long conversion consistent with its typed integer overflow
handling. Java's generic valueless overflow sentinels are a broader
semantic difference and are out of scope here.

## Are these changes tested?

Yes. New literal tests cover decimal values above and below the
`LongType` range.

## Are there any user-facing changes?

Yes. Decimal literal conversion to `LongType` now reports overflow with
the correct long sentinel type.

Co-authored-by: Abanoub Doss <abanoub.doss@gmail.com>

Author: abnobdoss

pyiceberg/expressions/literals.py

@@ -526,9 +526,9 @@ def _(self, _: IntegerType) -> Literal[int]:
     def _(self, _: LongType) -> Literal[int]:
         value_int = int(self.value.to_integral_value())
         if value_int > LongType.max:
-            return IntAboveMax()
+            return LongAboveMax()
         elif value_int < LongType.min:
-            return IntBelowMin()
+            return LongBelowMin()
         else:
             return LongLiteral(value_int)
 

tests/expressions/test_literals.py

@@ -40,6 +40,7 @@
     IntBelowMin,
     Literal,
     LongAboveMax,
+    LongBelowMin,
     LongLiteral,
     StringLiteral,
     TimeLiteral,
@@ -878,6 +879,14 @@ def test_string_to_long_large_scientific_notation_above_max() -> None:
     assert isinstance(literal("1e1000000").to(LongType()), LongAboveMax)
 
 
+def test_decimal_to_long_above_max() -> None:
+    assert isinstance(DecimalLiteral(Decimal(LongType.max + 1)).to(LongType()), LongAboveMax)
+
+
+def test_decimal_to_long_below_min() -> None:
+    assert isinstance(DecimalLiteral(Decimal(LongType.min - 1)).to(LongType()), LongBelowMin)
+
+
 def test_string_to_integer_type_invalid_value() -> None:
     with pytest.raises(ValueError) as e:
         _ = literal("abc").to(IntegerType())