dev: fix lint warnings introduced by #2062 (#2096)

> Hm. Sorry about the lint failures here, they slipped my attention
locally since they show up as warnings, not errors, in my editor. I'm
happy to put a PR fixing them later unless you get to it first.
>
> Not too sure how to deal with the unused DiagWorker::check method,
since it is used, just in a test-only module. We can certainly mark it
as #[cfg(test)] but that feels a little nasty.


https://github.com/Myriad-Dreamin/tinymist/pull/2062#issuecomment-3237812684

I ended up inlining the logic of `DiagWorker::check` into the test.

crates/tinymist-query/src/diagnostics.rs

@@ -46,16 +46,8 @@ impl<'w> DiagWorker<'w> {
         }
     }
 
-    /// Runs code check on the given document.
-    pub fn check(mut self, source: &Source) -> Self {
-        for diag in self.ctx.lint(&source) {
-            self.handle(&diag);
-        }
-        self
-    }
-
     /// Runs code check on the main document and all its dependencies.
-    pub fn full_check(mut self) -> Self {
+    pub fn check(mut self) -> Self {
         for dep in self.ctx.world.depended_files() {
             if WorkspaceResolver::is_package_file(dep) {
                 continue;