refactor: move library into it's own crate

lib_sync_core/src/lib.rs

@@ -0,0 +1,19 @@
+pub mod error;
+
+pub(crate) use error::*;
+pub mod task_manager;
+
+pub fn add(left: u64, right: u64) -> u64 {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}