fix(linter/eslint/require-await): count await using as an await (#27080)

## Root cause

`AwaitFinder`
(`crates/oxc_linter/src/rules/eslint/require_await.rs:220-239`) only
sets `found` for `await` expressions and `for await`. An `await using`
declaration also awaits (the resource's disposal when the scope exits),
so an async function whose only await is `await using x = ...` or `for
(await using x of xs)` is reported.

The rule's dangerous fix then removes `async`, which leaves `await
using` outside an async function. With oxlint 1.85.0:

```js
// input
export async function f() {
  await using x = getResource();
}

// after --fix-dangerously
export function f() {
  await using x = getResource();
}
```

The fixed file no longer parses (`` `await` is only allowed within async
functions and at the top levels of modules ``). In a debug build the
same fix trips the fixer's syntax check
(`crates/oxc_linter/src/fixer/mod.rs:422`).

ESLint counts these declarations since eslint/eslint#19828
([`lib/rules/require-await.js#L180-L182`](https://github.com/eslint/eslint/blob/6fb3685bcbe9a6f72fd7dfb9129686b6fb96b0bd/lib/rules/require-await.js#L180-L182)):

```js
if (node.kind === "await using") {
	scopeInfo.hasAwait = true;
}
```

## Notes

AI-assisted: I used Claude Code while investigating; I reviewed, ran and
verified every change myself.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Cameron <cameron.clark@hey.com>

crates/oxc_linter/src/rules/eslint/require_await.rs

@@ -2,10 +2,13 @@ use oxc_ast::{
     AstKind,
     ast::{
         ArrowFunctionExpression, AwaitExpression, ForOfStatement, Function, FunctionBody,
-        FunctionType, MethodDefinition, ObjectProperty, PropertyKey,
+        FunctionType, MethodDefinition, ObjectProperty, PropertyKey, VariableDeclaration,
     },
 };
-use oxc_ast_visit::{VisitJs, walk_js::walk_for_of_statement};
+use oxc_ast_visit::{
+    VisitJs,
+    walk_js::{walk_for_of_statement, walk_variable_declaration},
+};
 use oxc_diagnostics::OxcDiagnostic;
 use oxc_macros::declare_oxc_lint;
 use oxc_semantic::ScopeFlags;
@@ -233,6 +236,14 @@ impl<'a> VisitJs<'a> for AwaitFinder {
         }
     }
 
+    fn visit_variable_declaration(&mut self, decl: &VariableDeclaration<'a>) {
+        if decl.kind.is_await() {
+            self.found = true;
+        } else {
+            walk_variable_declaration(self, decl);
+        }
+    }
+
     fn visit_arrow_function_expression(&mut self, _expr: &ArrowFunctionExpression<'a>) {}
 
     fn visit_function(&mut self, _func: &Function<'a>, _flags: ScopeFlags) {}
@@ -287,6 +298,9 @@ fn test() {
            }
         };
         ",
+        "async function foo() { await using x = getResource() }",
+        "async function foo() { { await using x = getResource() } }",
+        "async function foo() { for (await using x of xs) {} }",
     ];
 
     let fail = vec![
@@ -300,6 +314,8 @@ fn test() {
         "(class { async ''() { doSomething() } })",
         "async function foo() { async () => { await doSomething() } }",
         "async function foo() { await (async () => { doSomething() }) }",
+        "async function foo() { using x = getResource() }",
+        "async function foo() { async () => { await using x = getResource() } }",
     ];
 
     let fix = vec![

crates/oxc_linter/src/snapshots/eslint_require_await.snap

@@ -71,3 +71,17 @@ source: crates/oxc_linter/src/tester.rs
    ·                               ─────────────────────────────
    ╰────
   help: Consider removing the `async` keyword.
+
+  ⚠ eslint(require-await): Async function has no `await` expression.
+   ╭─[require_await.mts:1:16]
+ 1 │ async function foo() { using x = getResource() }
+   ·                ───
+   ╰────
+  help: Consider removing the `async` keyword.
+
+  ⚠ eslint(require-await): Async function has no `await` expression.
+   ╭─[require_await.mts:1:16]
+ 1 │ async function foo() { async () => { await using x = getResource() } }
+   ·                ───
+   ╰────
+  help: Consider removing the `async` keyword.