fix: add windowsHide: true to spawn in runCommandWithTimeout

Fixes flashing conhost.exe windows on Windows when exec module spawns
child processes. The windowsHide: true option prevents orphaned conhost.exe
processes and eliminates disruptive terminal window flashing.

Closes #18613

src/process/exec.ts

@@ -139,6 +139,7 @@ export async function runCommandWithTimeout(
     cwd,
     env: resolvedEnv,
     windowsVerbatimArguments,
+    windowsHide: true,
     ...(shouldSpawnWithShell({ resolvedCommand, platform: process.platform })
       ? { shell: true }
       : {}),