fix(datetime): 修正 GaussDB 时间戳边界判断逻辑

- 引入常量 _GAUSSDB_MIN_MICROS 和 _GAUSSDB_MAX_MICROS 统一时间戳边界
- 替换原硬编码时间戳边界值，提升代码可维护性
- 调整测试用例中的格式和空行，保证代码风格一致
- 修复 GaussDB timestamp 和 timestamptz 类型的边界溢出错误处理逻辑

Author: 陈云亮

.gitignore

@@ -9,6 +9,8 @@ __pycache__/
 /gaussdb_binary/
 .vscode
 .venv
+myenv
+activate_dev.ps1
 .coverage
 htmlcov
 .idea

gaussdb/gaussdb/types/datetime.py

@@ -491,9 +491,9 @@ def load(self, data: Buffer) -> datetime:
         except OverflowError:
             # GaussDB 边界检查：根据实际的 micros 值判断错误类型
             # 年份1: -62135596800000000, 年份9999: ~253402300799999999
-            if micros < -62135596800000000:  # 小于年份1
+            if micros < self._GAUSSDB_MIN_MICROS:  # 小于年份1
                 raise DataError("timestamp too small (before year 1)") from None
-            elif micros > 253402300799999999:  # 大于年份9999
+            elif micros > self._GAUSSDB_MAX_MICROS:  # 大于年份9999
                 raise DataError("timestamp too large (after year 9999)") from None
             else:
                 raise DataError("timestamp too large (after year 10K)") from None
@@ -584,6 +584,9 @@ def _load_notimpl(self: TimestamptzLoader, data: Buffer) -> datetime:
 class TimestamptzBinaryLoader(Loader):
     format = Format.BINARY
 
+    # GaussDB 时间戳边界（微秒）
+    _GAUSSDB_MAX_MICROS = 253402300799999999  # 约9999年底
+
     def __init__(self, oid: int, context: AdaptContext | None = None):
         super().__init__(oid, context)
         self._timezone = get_tzinfo(self.connection.pgconn if self.connection else None)
@@ -613,7 +616,7 @@ def load(self, data: Buffer) -> datetime:
 
             if micros <= 0:
                 raise DataError("timestamp too small (before year 1)") from None
-            elif micros > 253402300799999999:  # GaussDB 9999年边界
+            elif micros > self._GAUSSDB_MAX_MICROS:  # GaussDB 9999年边界
                 raise DataError("timestamp too large (after year 9999)") from None
             else:
                 raise DataError("timestamp too large (after year 10K)") from None

tests/types/test_datetime.py

@@ -89,7 +89,7 @@ def test_load_date(self, conn, val, expr, fmt_out):
         except Exception as e:
             pytest.skip(f"Database does not support this date format: {e}")
             return
-        
+
         expected = as_date(val)
         # GaussDB 可能返回 datetime 而非 date
         if isinstance(result, dt.datetime) and not isinstance(expected, dt.datetime):
@@ -147,7 +147,7 @@ def test_load_overflow_message_binary(self, conn, val, msg):
         # GaussDB 不支持 infinity 日期
         if "infinity" in val.lower():
             pytest.skip("GaussDB does not support infinity dates")
-        
+
         try:
             cur = conn.cursor(binary=True)
             cur.execute("select %s::date", (val,))