fix(integration): honour the stdout/stderr write callback in the command runner

The capture function replacing process.stdout.write and process.stderr.write
took only the chunk, so a caller using write(chunk, cb) or
write(chunk, encoding, cb) never had its callback invoked. Anything waiting on
that callback would stall for the duration of the command under test.

Addresses Copilot review on PR #235.

Co-Authored-By: Harshi Shah <harshi.shah@contentstack.com>

Author: SakshiKoli-CS

test/integration/harness/run-command.ts

@@ -32,8 +32,10 @@ export async function runCommand(
   argv: string[],
 ): Promise<CommandResult> {
   const chunks: string[] = [];
-  const capture = (chunk: any): boolean => {
+  const capture = (chunk: any, encoding?: any, callback?: any): boolean => {
     chunks.push(typeof chunk === 'string' ? chunk : Buffer.from(chunk).toString('utf8'));
+    const done = typeof encoding === 'function' ? encoding : callback;
+    if (typeof done === 'function') done();
     return true;
   };