feat: 新增多项核心功能并优化默认执行策略

1.  将CliRunner默认执行策略从sequential改为dependency
2.  新增RunReport的任务状态查询和时长统计方法
3.  实现task装饰器并补充executor参数文档
4.  新增进程池执行器支持CPU密集型任务
5.  新增Graph.chain链式构建和add_subgraph子图合并功能
6.  新增流式任务传递、进程池执行、命名空间等多类测试用例
7.  补充tests目录路径导入配置

tests/test_chain_dsl.py

@@ -0,0 +1,101 @@
+"""Tests for Graph.chain DSL."""
+
+from __future__ import annotations
+
+import pyflowx as px
+from pyflowx.task import TaskSpec
+
+
+def _fn() -> None:
+    return None
+
+
+def test_chain_basic_linkage() -> None:
+    """chain(a, b, c) 应建立 a->b->c 依赖."""
+    a = TaskSpec("a", _fn)
+    b = TaskSpec("b", _fn)
+    c = TaskSpec("c", _fn)
+
+    graph = px.Graph().chain(a, b, c)
+
+    assert graph.all_specs()["b"].depends_on == ("a",)
+    assert graph.all_specs()["c"].depends_on == ("b",)
+    assert graph.all_specs()["a"].depends_on == ()
+
+
+def test_chain_single_spec() -> None:
+    """chain(a) 应只注册 a，无依赖."""
+    a = TaskSpec("a", _fn)
+    graph = px.Graph().chain(a)
+    assert "a" in graph
+    assert graph.all_specs()["a"].depends_on == ()
+
+
+def test_chain_preserves_existing_deps() -> None:
+    """chain 应保留 spec 已有的 depends_on."""
+    a = TaskSpec("a", _fn)
+    b = TaskSpec("b", _fn)
+    c = TaskSpec("c", _fn, depends_on=("b",))
+
+    graph = px.Graph().chain(a, b, c)
+    # c 已有 depends_on=('b',)，前驱是 b，已在依赖中，不重复添加
+    assert graph.all_specs()["c"].depends_on == ("b",)
+
+
+def test_chain_merges_existing_deps() -> None:
+    """chain 应将前驱追加到已有依赖前（若不存在）."""
+    a = TaskSpec("a", _fn)
+    x = TaskSpec("x", _fn)
+    c = TaskSpec("c", _fn, depends_on=("x",))
+
+    graph = px.Graph().chain(a, x, c)
+    # c 前驱是 x，但 c 已依赖 x，不重复
+    assert graph.all_specs()["c"].depends_on == ("x",)
+
+
+def test_chain_returns_self() -> None:
+    """chain 返回 self 支持链式调用."""
+    a = TaskSpec("a", _fn)
+    graph = px.Graph()
+    assert graph.chain(a) is graph
+
+
+def test_chain_execution_order() -> None:
+    """chain 应保证执行顺序."""
+    order: list[str] = []
+
+    def make(name: str):
+        def fn() -> str:
+            order.append(name)
+            return name
+        return fn
+
+    a = TaskSpec("a", make("a"))
+    b = TaskSpec("b", make("b"))
+    c = TaskSpec("c", make("c"))
+
+    graph = px.Graph().chain(a, b, c)
+    report = px.run(graph)
+    assert report.success
+    assert order == ["a", "b", "c"]
+
+
+def test_chain_with_decorator_specs() -> None:
+    """chain 应与 @task 装饰器配合."""
+
+    @px.task
+    def extract() -> int:
+        return 1
+
+    @px.task
+    def transform(extract: int) -> int:
+        return extract + 10
+
+    @px.task
+    def load(transform: int) -> int:
+        return transform + 100
+
+    graph = px.Graph().chain(extract, transform, load)
+    report = px.run(graph)
+    assert report.success
+    assert report["load"] == 111