refactor: move task_fn into its own crate

dagx-test/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "dagx-test"
+version = "0.3.1"
+edition = "2021"
+rust-version = "1.81"
+authors = ["TechnoPorg"]
+license = "MIT"
+description = "Utilities for dagx's internal tests"
+repository = "https://github.com/swaits/dagx"
+homepage = "https://github.com/swaits/dagx"
+documentation = "https://docs.rs/dagx-test"
+
+[lints]
+workspace = true
+
+[dependencies]
+dagx = { version = "0.3.1", path = "../" }