Fix event handler type and Promise handling in query-server-client

This commit fixes incorrect type signatures and Promise handling for
query server event handlers that were causing ESLint errors.

Problem:
The queryServerStartListeners were typed to return 'void', but actual
usage in the codebase shows they can be async functions returning
'Promise<void>'. This mismatch caused two issues:

1. Type mismatch: The onStart() method in query-runner.ts accepts
   callbacks typed as '(progress) => Promise<void>', but the listener
   registration was typed as '(progress) => void'

2. ESLint error at line 163: When calling Promise.all() on the array
   of handler results, ESLint detected that handlers might return void
   instead of Promise, triggering '@typescript-eslint/await-thenable':
   'Unexpected iterable of non-Promise values passed to promise
   aggregator'

Solution:
1. Update type signatures to allow both synchronous (void) and
   asynchronous (Promise<void>) handlers:
   - Changed listener array type from '() => void' to
     '() => void | Promise<void>'
   - Updated onDidStartQueryServer parameter type to match

2. Wrap handler invocations in Promise.resolve() to ensure they always
   return a Promise, regardless of whether the handler is sync or async:
   - Changed: handler(progress)
   - To: Promise.resolve(handler(progress))

This makes Promise.all() safe to use with mixed sync/async handlers
while maintaining backward compatibility with existing code.

File modified:
- extensions/ql-vscode/src/query-server/query-server-client.ts

Author: d10c

extensions/ql-vscode/src/query-server/query-server-client.ts

@@ -52,14 +52,14 @@ export class QueryServerClient extends DisposableObject {
   withProgressReporting: WithProgressReporting;
 
   private readonly queryServerStartListeners = [] as Array<
-    (progress: ProgressCallback) => void
+    (progress: ProgressCallback) => void | Promise<void>
   >;
 
   // Can't use standard vscode EventEmitter here since they do not cause the calling
   // function to fail if one of the event handlers fail. This is something that
   // we need here.
   readonly onDidStartQueryServer = (
-    e: (progress: ProgressCallback) => void,
+    e: (progress: ProgressCallback) => void | Promise<void>,
   ) => {
     this.queryServerStartListeners.push(e);
   };
@@ -160,7 +160,9 @@ export class QueryServerClient extends DisposableObject {
     // Ensure we await all responses from event handlers so that
     // errors can be properly reported to the user.
     await Promise.all(
-      this.queryServerStartListeners.map((handler) => handler(progress)),
+      this.queryServerStartListeners.map((handler) =>
+        Promise.resolve(handler(progress)),
+      ),
     );
   }