major overhaul of Backend from dynamic to static dispatch using an big enum

crates/pacdef/src/backend/actual/rust.rs

@@ -12,7 +12,19 @@ use crate::{Group, Package};
 
 #[derive(Debug, Clone)]
 pub struct Rust {
-    pub(crate) packages: HashSet<Package>,
+    pub packages: HashSet<Package>,
+}
+impl Rust {
+    pub fn new() -> Self {
+        Self {
+            packages: HashSet::new(),
+        }
+    }
+}
+impl Default for Rust {
+    fn default() -> Self {
+        Self::new()
+    }
 }
 
 const BINARY: Text = "cargo";
@@ -76,14 +88,6 @@ fn extract_packages(json: &Value) -> Result<HashSet<Package>> {
     Ok(result)
 }
 
-impl Rust {
-    pub(crate) fn new() -> Self {
-        Self {
-            packages: HashSet::new(),
-        }
-    }
-}
-
 fn get_crates_file() -> Result<PathBuf> {
     let mut result = crate::path::get_cargo_home().context("getting cargo home dir")?;
     result.push(".crates2.json");