Reads and writes with a zero timeout need to be non-blocking.

[NathanFreeman]

No description provided.

[matyhtf]

Thanks for the fix. Please address the following issues before merging.

1. Preserve native PHP behavior for zero-timeout writes

For a blocking TCP stream with stream_set_timeout($stream, 0, 0), once its send buffer is full, I reproduced the following difference on Linux / PHP 8.4:

Behavior	Native PHP	This PR
fwrite()	false	0
stream_get_meta_data($stream)['timed_out']	true	false

In socket_write(), the new condition routes a blocking stream with zero timeout through send_once(), but the existing error handling converts EAGAIN into a zero-byte write. This loses the distinction between a blocking stream whose timeout has expired and an explicitly non-blocking stream. Applications checking for false or timed_out may keep retrying.

Please keep the immediate write attempt, but preserve native PHP's failure return and timeout state when a blocking zero-timeout write cannot proceed. Explicitly non-blocking streams should retain their zero-byte-write behavior. See PHP's socket stream write implementation.

2. Make the write regression test actually reach a full send buffer

The current test writes only 1 MiB once. On my machine, all 1 MiB was written immediately, so the test never exercised the full-buffer condition. Its assertion also accepts false, 0, and a complete write, which cannot detect the compatibility issue above.

Please fill the buffer in non-blocking mode until no further bytes can be written, then switch back to blocking mode, set the zero timeout, and verify the write result, timed_out, and eof against native PHP. Cover explicitly non-blocking writes separately.

Please also replace the fixed 10-second server sleep with explicit synchronization, and bound the polling loop in the read test so that a regression cannot hang the test indefinitely.

The read-side approach is consistent with native PHP. The four new tests and the existing coroutine timeout test passed in my Linux / PHP 8.4 build, but the additional native-PHP comparison exposed the write-side gap above.