fix(stats): don't require all fields under [stats] (#1437)

Before this change, when configuring only `common_subcommands` and
not `common_prefix` (so it would take its default value),
atuin produces an error message:
```
Error: could not load client settings  Caused by:     failed to deserialize: missing field `common_prefix`  Location:     atuin-client/src/settings.rs:456:26
Error: could not load client settings

Caused by:
    failed to deserialize: missing field `common_prefix`

Location:
    atuin-client/src/settings.rs:456:26
Error:: command not found
```

With this change, the fields can be specified separately and missing
fields will take their default values.

atuin-client/src/settings.rs

@@ -145,18 +145,30 @@ pub enum WordJumpMode {
 
 #[derive(Clone, Debug, Deserialize)]
 pub struct Stats {
+    #[serde(default = "Stats::common_prefix_default")]
     pub common_prefix: Vec<String>, // sudo, etc. commands we want to strip off
+    #[serde(default = "Stats::common_subcommands_default")]
     pub common_subcommands: Vec<String>, // kubectl, commands we should consider subcommands for
 }
 
+impl Stats {
+    fn common_prefix_default() -> Vec<String> {
+        vec!["sudo", "doas"].into_iter().map(String::from).collect()
+    }
+
+    fn common_subcommands_default() -> Vec<String> {
+        vec!["cargo", "go", "git", "npm", "yarn", "pnpm", "kubectl"]
+            .into_iter()
+            .map(String::from)
+            .collect()
+    }
+}
+
 impl Default for Stats {
     fn default() -> Self {
         Self {
-            common_prefix: vec!["sudo", "doas"].into_iter().map(String::from).collect(),
+            common_prefix: Self::common_prefix_default(),
-            common_subcommands: vec!["cargo", "go", "git", "npm", "yarn", "pnpm", "kubectl"]
+            common_subcommands: Self::common_subcommands_default(),
-                .into_iter()
-                .map(String::from)
-                .collect(),
         }
     }
 }