feat: add extension_paths parameter for loading Chrome extensions (#210)

Add `extension_paths` parameter to all launch functions (Python + JS) for loading Chrome extensions.

Resolves paths to absolute, injects `--load-extension` and `--disable-extensions-except` flags via `build_args()`.

Note: Extensions require a persistent context (`launch_persistent_context`) to function — this is a Chromium limitation.

Co-authored-by: zackycodes <75211659+zackycodes@users.noreply.github.com>

js/tests/extension-loading.test.ts

@@ -0,0 +1,16 @@
+import path from "path";
+import { _buildArgsForTest } from "../src/playwright.js";
+
+test("extension paths inject chrome flags", () => {
+  const args = _buildArgsForTest({
+    extensionPaths: ["./ext"],
+  });
+
+  const abs = path.resolve("./ext");
+
+  expect(args).toContain(`--load-extension=${abs}`);
+
+  expect(args).toContain(
+    `--disable-extensions-except=${abs}`
+  );
+});