M1: core engine, config, plugin model and core plugins

- Cargo workspace (core, plugins, tui, cli) with drop-in compatible CLI
- Python-compatible config file handling, limits, views, rates, MMM, history
- process collection via sysinfo + procfs, filters, thresholds, events, actions
- 20 core plugins (cpu, percpu, mem, memswap, load, fs, network, diskio, ...)
- stdout, stdout-csv, stdout-json, --issue, --modules-list output modes
- differential test harness against the Python implementation

crates/glances-tui/src/lib.rs

@@ -0,0 +1,14 @@
+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);
+    }
+}