chore(m197): 清掉 clippy 的三处拒绝 + 一处 2018 idioms 警告

CI 的门禁是 `cargo clippy --workspace --all-targets -- -D warnings`：
冗余闭包 / 用例表的类型复杂度 / Default 之后逐字段赋值 / elided lifetime 四处都会红。
纯实现侧改动，行为不变（757 + 31 全绿）。

crates/app-iced/src/pages/settings/java/downloads/tests.rs

@@ -235,7 +235,10 @@ fn every_download_template_renders_without_leftover_placeholders() {
     use unlucky_i18n::{Key, Lang};
 
     let catalog = Lang::En.catalog();
-    let cases: [(&str, Key, &[(&str, &str)]); 6] = [
+    /// 一条用例：标签 / key / 渲染参数。
+    type Case<'a> = (&'a str, Key, &'a [(&'a str, &'a str)]);
+
+    let cases: [Case<'_>; 6] = [
         (
             "failed",
             Key::SettingsJavaDownloadFailed,

crates/app-iced/src/pages/settings/java/prefs_store.rs

@@ -100,7 +100,7 @@ pub fn effective(config: &Path, prefs: &Prefs) -> Effective {
         let text = prefs.saved_install_root.trim();
         (!text.is_empty()).then(|| PathBuf::from(text))
     };
-    let layout = home_of(config).map(|home| LauncherLayout::new(home));
+    let layout = home_of(config).map(LauncherLayout::new);
     let (root, root_mode, root_layer, root_unresolved) = match &layout {
         Some(layout) => match JavaInstallRoot::resolve(
             data_mode,

crates/app-iced/src/pages/settings/java/tests/prefs.rs

@@ -40,11 +40,13 @@ fn the_three_keys_are_written_and_read_back() {
     let dir = root("prefs-save");
     let file = config(&dir);
 
-    let mut prefs = Prefs::default();
     // 前后带空格：落盘值会被 trim，回读的草稿必须显示**磁盘上那份**。
-    prefs.install_root = "  D:/JDKs  ".to_string();
-    prefs.auto_install = false;
-    prefs.priority = vec!["zulu", "temurin"];
+    let mut prefs = Prefs {
+        install_root: "  D:/JDKs  ".to_string(),
+        auto_install: false,
+        priority: vec!["zulu", "temurin"],
+        ..Prefs::default()
+    };
     assert!(prefs.dirty(), "改过三键就该是脏的");
 
     let snapshot = prefs_store::save(&file, &prefs).expect("三键应能落盘");