feat: 增加板块信息（block_info）获取与解析功能

1. 核心模型：增加 TdxBlock dataclass。
2. 协议命令：实现 GetBlockInfoMetaCmd 与 GetBlockInfoCmd。
3. 编解码器：增加 codec/block.py，支持 .dat 板块文件二进制解析。
4. 客户端 API：TdxClient 和 AsyncTdxClient 增加 get_block_info()，支持分片拉取。
5. 测试与验证：增加单元测试 tests/unit/test_block_info.py 及实测脚本。
6. 文档更新：README.md 同步 API 及安装说明。

tests/unit/test_block_info.py

@@ -0,0 +1,106 @@
+"""板块信息单元测试。"""
+
+import pytest
+import struct
+from unittest.mock import MagicMock, patch
+
+from xmtdx.client import AsyncTdxClient, TdxClient
+
+
+@patch("xmtdx.client.AsyncTdxConnection")
+def test_async_get_block_info_logic(mock_conn_cls):
+    """测试 AsyncTdxClient.get_block_info 的异步拉取逻辑。"""
+    mock_conn = mock_conn_cls.return_value
+    
+    # 模拟异步 execute
+    async def mock_execute(cmd):
+        from xmtdx.commands.block_info import GetBlockInfoMetaCmd, GetBlockInfoCmd
+        if isinstance(cmd, GetBlockInfoMetaCmd):
+            return 100, "hash"
+        if isinstance(cmd, GetBlockInfoCmd):
+            return b"B" * min(cmd.length, 100 - cmd.start)
+        return None
+
+    mock_conn.execute.side_effect = mock_execute
+    mock_conn.connect.return_value = None
+    mock_conn.close.return_value = None
+
+    async def main():
+        client = AsyncTdxClient("127.0.0.1")
+        with patch("xmtdx.client.parse_block_dat") as mock_parse:
+            mock_parse.return_value = []
+            res = await client.get_block_info("test.dat")
+            
+            assert isinstance(res, list)
+            assert mock_conn.execute.call_count == 2 # 1 meta + 1 data
+
+    import asyncio
+    asyncio.run(main())
+from xmtdx.codec.block import parse_block_dat
+from xmtdx.models.finance import TdxBlock
+
+
+def test_parse_block_dat_empty():
+    assert parse_block_dat(b"") == []
+    assert parse_block_dat(b"A" * 385) == []
+
+
+def test_parse_block_dat_basic():
+    # 构造一个极小的合法 .dat 文件
+    # Header 384 + Count 2 + Record 2813
+    data = bytearray(384)
+    data.extend(struct.pack("<H", 1))  # 1 block
+    
+    # Block Record: 9s (name) + H (count) + H (type) + 2800s (codes)
+    name = "测试板块".encode("gbk")
+    record = bytearray((name + b"\x00" * 9)[:9])
+    record.extend(struct.pack("<HH", 2, 1))  # 2 stocks, type 1
+    
+    # 2 stocks: 600000, 000001
+    codes = "600000\x00000001\x00".encode("ascii")
+    record.extend((codes + b"\x00" * 2800)[:2800])
+    
+    data.extend(record)
+    
+    blocks = parse_block_dat(bytes(data), "block_gn.dat")
+    
+    assert len(blocks) == 1
+    b = blocks[0]
+    assert b.name == "测试板块"
+    assert b.count == 2
+    assert b.category == 2  # 'gn' in filename -> 2
+    assert b.codes == ["600000", "000001"]
+
+
+@patch("xmtdx.client.TdxConnection")
+def test_get_block_info_logic(mock_conn_cls):
+    """测试 TdxClient.get_block_info 的分片拉取逻辑。"""
+    mock_conn = mock_conn_cls.return_value
+    
+    client = TdxClient("127.0.0.1")
+    
+    # 模拟 GetBlockInfoMeta 响应：size=35000 (需要2次拉取)
+    def mock_execute(cmd):
+        from xmtdx.commands.block_info import GetBlockInfoMetaCmd, GetBlockInfoCmd
+        if isinstance(cmd, GetBlockInfoMetaCmd):
+            return 35000, "dummy_hash"
+        if isinstance(cmd, GetBlockInfoCmd):
+            # 返回对应长度的填充数据
+            return b"A" * min(cmd.length, 35000 - cmd.start)
+        return None
+
+    mock_conn.execute.side_effect = mock_execute
+    
+    # 我们主要测试循环是否正确
+    with patch("xmtdx.client.parse_block_dat") as mock_parse:
+        mock_parse.return_value = [TdxBlock("Test", 1, 0, [])]
+        res = client.get_block_info("test.dat")
+        
+        assert len(res) == 1
+        # 应该调用了 1 (meta) + 2 (data: 30000 + 5000) = 3 次 execute
+        assert mock_conn.execute.call_count == 3
+        
+        # 验证最后一次拉取的参数
+        last_call_args = mock_conn.execute.call_args_list[-1][0][0]
+        assert last_call_args.start == 30000
+        assert last_call_args.length == 30000