feat: JsonWriter/JsonReader 支持 DateTime 字段(序列化为 yyyy-MM-dd HH:mm:ss 字符串,可反序列化回,含 Option<DateTime>)

src/json/JsonReader.cj

@@ -12,6 +12,7 @@ package simcu::serialization.json
 import std.collection.*
 import std.convert.*
 import std.reflect.*
+import std.time.*
 import stdx.encoding.json.*
 import simcu::serialization.common.ReflectionCache
 import simcu::serialization.common.FieldMetadata
@@ -62,6 +63,7 @@ public class JsonReader {
             case "Float64" => return readFloat64(value)
             case "Float32" => return Float32(readFloat64(value))
             case "Rune" => return readChar(value)
+            case "DateTime" | "std.time.DateTime" => return readDateTime(value)
             case _ => ()
         }
 
@@ -298,6 +300,15 @@ public class JsonReader {
         throw Exception("JsonSerializer: 无法转换为 Char")
     }
 
+    private static func readDateTime(v: JsonValue): DateTime {
+        let s = readString(v)
+        try {
+            return DateTime.parse(s, "yyyy-MM-dd HH:mm:ss")
+        } catch (_: Exception) {
+            throw Exception("JsonSerializer: 无法转换为 DateTime: ${s}")
+        }
+    }
+
     /// 生成某类型的占位默认值（用于构造 Option<X> 的 None：None 的参数槽类型是 X）。
     private static func defaultValueFor(typeName: String): Any {
         match (typeName) {
@@ -314,6 +325,7 @@ public class JsonReader {
             case "Float64" => return Float64(0.0)
             case "Float32" => return Float32(0.0)
             case "Rune" => return Rune(0)
+            case "DateTime" | "std.time.DateTime" => return DateTime.parse("1970-01-01 00:00:00", "yyyy-MM-dd HH:mm:ss")
             case _ => ()
         }
         // 集合/对象/枚举：反射无参构造；失败则抛异常