feat: add std.is_even, std.is_odd, std.is_integer and std.is_decimal

Upstream issue: google/go-jsonnet#702

crates/jrsonnet-stdlib/src/lib.rs

@@ -105,6 +105,10 @@ pub fn stdlib_uncached(settings: Rc<RefCell<Settings>>) -> ObjValue {
 		("mantissa", builtin_mantissa::INST),
 		("exponent", builtin_exponent::INST),
 		("round", builtin_round::INST),
+		("isEven", builtin_is_even::INST),
+		("isOdd", builtin_is_odd::INST),
+		("isInteger", builtin_is_integer::INST),
+		("isDecimal", builtin_is_decimal::INST),
 		// Operator
 		("mod", builtin_mod::INST),
 		("primitiveEquals", builtin_primitive_equals::INST),

crates/jrsonnet-stdlib/src/math.rs

@@ -119,3 +119,23 @@ pub fn builtin_exponent(x: f64) -> i16 {
 pub fn builtin_round(x: f64) -> f64 {
 	x.round()
 }
+
+#[builtin]
+pub fn builtin_is_even(x: f64) -> bool {
+	builtin_round(x) % 2.0 == 0.0
+}
+
+#[builtin]
+pub fn builtin_is_odd(x: f64) -> bool {
+	builtin_round(x) % 2.0 == 1.0
+}
+
+#[builtin]
+pub fn builtin_is_integer(x: f64) -> bool {
+	builtin_round(x) == x
+}
+
+#[builtin]
+pub fn builtin_is_decimal(x: f64) -> bool {
+	builtin_round(x) != x
+}