fix: use epsilon tolerance in multipleOf float validation (#989)

math.Mod produces tiny non-zero remainders for valid floats like
0.36 % 0.01 due to IEEE 754 precision, causing false negatives.

Refs: #988

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: smazurov

validate.go

@@ -493,7 +493,7 @@ func Validate(r Registry, s *Schema, path *PathBuffer, mode ValidateMode, v any,
 			}
 		}
 		if s.MultipleOf != nil {
-			if math.Mod(num, *s.MultipleOf) != 0 {
+			if r := math.Mod(num, *s.MultipleOf); math.Abs(r) > 1e-9 && math.Abs(r-*s.MultipleOf) > 1e-9 {
 				res.Add(path, v, s.msgMultipleOf)
 			}
 		}

validate_test.go

@@ -212,6 +212,13 @@ var validateTests = []struct {
 		input: map[string]any{"value": 2},
 		errs:  []string{"expected number to be a multiple of 5"},
 	},
+	{
+		name: "multiple of float success",
+		typ: reflect.TypeFor[struct {
+			Value float64 "json:\"value\" multipleOf:\"0.01\""
+		}](),
+		input: map[string]any{"value": 0.36},
+	},
 	{
 		name:  "string success",
 		typ:   reflect.TypeFor[string](),