feat: 重构项目结构并添加核心功能

refactor: 将代码按功能模块重新组织到 core/runtime/control 等目录
feat(core): 添加 Context、FlowNode 等核心 trait 和类型
feat(runtime): 实现 FlowEngine 和状态管理
feat(control): 添加顺序/并行/条件控制流节点
feat(nodes): 实现 HTTP/DB/MQ 等业务节点
docs: 更新 README 添加架构说明和快速开始示例
test: 添加性能测试脚本和示例代码

dsl-flow/Cargo.toml

@@ -0,0 +1,39 @@
+[package]
+name = "dsl-flow"
+version = "0.1.0"
+edition = "2021"
+license = "MIT"
+description = "A Rust DSL-based workflow engine supporting stateful/stateless flows, async nodes, fork-join, and extensible expression engines (Rhai/JS)."
+readme = "README.md"
+
+[lib]
+name = "dsl_flow"
+path = "src/lib.rs"
+
+[features]
+default = ["rhai", "http"]
+rhai = ["dep:rhai"]
+js = ["dep:boa_engine"]
+http = ["dep:reqwest"]
+
+[dependencies]
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "sync", "time"] }
+futures = "0.3"
+serde = { version = "1.0", features = ["derive"] }
+serde_json = { version = "1.0" }
+thiserror = "1.0"
+async-trait = "0.1"
+uuid = { version = "1", features = ["v4"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["fmt", "env-filter"] }
+
+# Optional engines and nodes
+rhai = { version = "1", optional = true, features = ["serde", "sync"] }
+boa_engine = { version = "0.20", optional = true }
+reqwest = { version = "0.12", optional = true, features = ["json", "rustls-tls"] }
+
+[dev-dependencies]
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "sync", "time"] }
+httpmock = "0.7"
+anyhow = "1.0"
+