Initialize project with Cargo.toml and basic structure

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+# just_template
+
+> a tool for code gen via templates
+
+## Template File Writing Rules
+
+`just_template` gens repetitive code using three core concepts: `impl_mark`, `impl_area`, and `param`.
+
+1. impl_mark
+   Mark an "impl point" with a line starting with 10 `>` chars: `>>>>>>>>>> NAME`.
+   Used for positioning. The system extracts the matching `impl_area` content and expands it here.
+
+2. impl_area
+   Declare a reusable code template:
+   `@@@ NAME >>>`
+   [template content]
+   `@@@ <<<`
+   Inside, use param placeholders like `<<<PARAM>>>`.
+   When adding an impl via cmd (e.g., `insert_impl!`), the system copies the area, replaces params, and appends to the impl_mark.
+
+3. param
+   - Params outside an impl_area are replaced globally.
+   - Params inside are replaced per-impl when generating.
+
+Example:
+
+Template:
+```rust
+// Auto generated
+use std::collections::HashMap;
+
+pub async fn my_func(
+    name: &str,
+    data: &[u8],
+    params: &HashMap<String, String>,
+) -> Option<Result<Vec<u32>, std::io::Error>> {
+    match name {
+>>>>>>>>>> arms
+@@@ >>> arms
+        "<<<crate_name>>>" => Some(<<<crate_name>>>::exec(data, params).await),
+@@@ <<<
+        _ => None,
+    }
+}
+```
+
+Run cmds:
+```rust
+insert_impl!("arms", crate_name = "my")
+insert_impl!("arms", crate_name = "you")
+```
+
+The `arms` impl_area becomes:
+```rust
+        "my" => Some(my::exec(data, params).await),
+        "you" => Some(you::exec(data, params).await),
+```
+
+Final expanded code:
+```rust
+// Auto generated
+use std::collections::HashMap;
+
+pub async fn my_func(
+    name: &str,
+    data: &[u8],
+    params: &HashMap<String, String>,
+) -> Option<Result<Vec<u32>, std::io::Error>> {
+    match name {
+        "my" => Some(my::exec(data, params).await),
+        "you" => Some(you::exec(data, params).await),
+        _ => None,
+    }
+}
+```
+
+## License
+
+This project is dual-licensed under MIT and Apache 2.0.
+See the LICENSE file for details.