fix: don't treat a finished request's write as an aborted connection

[dunglas]

Summary

go_ub_write() reported any PHP output write that happens after fastcgi_finish_request()/frankenphp_finish_request() as an aborted connection (0 bytes written, closed=true), regardless of whether the client was actually still connected. frankenphp_ub_write() then calls php_handle_aborted_connection() for that write, which:

• marks connection_status() as aborted even though the request finished normally, and
• when ignore_user_abort is off (PHP's default outside worker mode), calls zend_bailout(), silently terminating the rest of the script right at that output statement.

Worker mode forces ignore_user_abort=1 on every request, which is why this doesn't visibly crash a worker script — it only corrupts connection_status() there. Outside worker mode, any code that echoes/outputs anything after fastcgi_finish_request() gets silently truncated.

Fix

Discard the write (the responseWriter may no longer be safe to touch, see #2535/#2538), but report the actual client-disconnect status via fc.clientHasClosed() instead of hardcoding true.

Reproducer

<?php
echo "Before";
fastcgi_finish_request();
echo "After";

In classic (non-worker) mode with default ignore_user_abort, echo "After" triggers the bailout and any code after it never runs.

Tests

• Extended TestFinishRequest (testdata/finish-request.php) to log a line after the discarded write and assert it's reached — hangs on the unpatched code (module mode), passes with the fix.
• TestConnectionAbort still passes, confirming a genuine client disconnect is still correctly reported after fastcgi_finish_request().

Fixes #2548.