CLI: output is held until the script exits (flush()/fflush() have no effect)

[NikitaSomik]

phpr prints nothing until the script ends: everything written with echo,
fwrite(STDOUT), php://stdout or php://output is kept in memory and
written at exit, and flush() / fflush(STDOUT) don't change that. If the
process is killed, the output is lost. Writing to /dev/stdout or STDERR
comes out immediately.

This breaks interactive CLI programs (TUI games, prompts), progress output
and long-running scripts that stream logs.

Reproduce

<?php
echo "tick 1\n";
flush();
sleep(2);
echo "tick 2\n";

phpr flush.php | while IFS= read -r l; do echo "$l at +${SECONDS}s"; done

• PHP 8.5.7: tick 1 appears immediately, tick 2 two seconds later.
• phpr: both lines appear together after two seconds.

The cause seems to be crates/php-cli/src/main.rs, which writes
outcome.rendered to stdout only after run_source_with_argv returns.

Found while running a terminal Snake game (plain PHP 8.4+) on phpr. The game
itself passes its PHPUnit suite and produces identical benchmark checksums on
phpr; only the interactive mode is affected. A local workaround (an output
buffer flushed to fopen('/dev/stdout')) makes it playable.

Environment: macOS 26.6.2 (Apple M1 Pro), Rust 1.96.0, commit 352d4129.