Fix through2 v5 migration

Use the new objectTransform API and align the transform callback with the v5
types. Replace the deprecated through2 stub types with the readable-stream
types required by through2's declarations.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 8a4f7856-b291-4191-a8af-e2b410a8c01f

Author: cklin

extensions/ql-vscode/gulpfile.ts/textmate.ts

@@ -1,6 +1,6 @@
 import { dest, src } from "gulp";
 import { load } from "js-yaml";
-import { obj } from "through2";
+import { objectTransform } from "through2";
 import PluginError from "plugin-error";
 import type Vinyl from "vinyl";
 import type {
@@ -247,11 +247,11 @@ function transformFile(yaml: ExtendedTextmateGrammar<ExtendedMatchType>) {
 }
 
 export function transpileTextMateGrammar() {
-  return obj(
+  return objectTransform(
     (
       file: Vinyl,
       _encoding: string,
-      callback: (err: string | null, file: Vinyl | PluginError) => void,
+      callback: (err?: Error | null, file?: Vinyl) => void,
     ): void => {
       if (file.isNull()) {
         callback(null, file);
@@ -266,7 +266,6 @@ export function transpileTextMateGrammar() {
         callback(null, file);
       } else {
         callback(
-          "error",
           new PluginError("transpileTextMateGrammar", "Format not supported."),
         );
       }

extensions/ql-vscode/package-lock.json

@@ -2138,12 +2138,12 @@
     "@types/proper-lockfile": "^4.1.4",
     "@types/react": "^19.2.17",
     "@types/react-dom": "^19.2.3",
+    "@types/readable-stream": "^4.0.24",
     "@types/sarif": "^2.1.2",
     "@types/semver": "^7.7.1",
     "@types/stream-json": "^1.7.8",
     "@types/styled-components": "^5.1.11",
     "@types/tar-stream": "^3.1.4",
-    "@types/through2": "^5.0.0",
     "@types/tmp": "^0.2.6",
     "@types/vscode": "1.90.0",
     "@types/yauzl": "^3.4.0",