Handle errors when deleting dev-mode PID file on exit

The `onExited` listener in `writePidIfInDevMode` is `async`, but VS Code
`Event` listeners are fire-and-forget: the returned promise is never
awaited. As Copilot noted on #5515, that means a rejection from
`fs.delete(...)` would surface as an unhandled promise rejection, and the
debug log would be skipped on failure.

I kept the `async`/`await` form for readability and wrapped the body in
`try`/`catch` so nothing escapes: a fully-caught async body resolves
normally, and any failure is now logged via `this.logger.writeError`
instead of going unhandled. The original `main` version floated the
delete promise and logged success unconditionally, swallowing errors.

Drafted by Copilot (Claude Opus 4.8).

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

Author: andyleejordan

src/session.ts

@@ -387,8 +387,14 @@ export class SessionManager implements Middleware {
         await fs.writeFile(pidFilePath, Buffer.from(pid));
         const deletePidOnExit = pwshProcess.onExited(async () => {
             deletePidOnExit.dispose();
-            await fs.delete(pidFilePath, { useTrash: false });
-            this.logger.writeDebug(`Deleted PID file: ${pidFilePath}`);
+            try {
+                await fs.delete(pidFilePath, { useTrash: false });
+                this.logger.writeDebug(`Deleted PID file: ${pidFilePath}`);
+            } catch (err) {
+                this.logger.writeError(
+                    `Error occurred while deleting PID file:\n${err}`,
+                );
+            }
         });
         this.registeredCommands.push(deletePidOnExit);
         this.extensionContext.subscriptions.push(deletePidOnExit);