PHP_STREAM_OPTION_READ_TIMEOUT is also used for socket write timeouts #23978

Description

stream_set_timeout() passes PHP_STREAM_OPTION_READ_TIMEOUT to the stream wrapper:

The constant and its comment explicitly describe a read timeout:

However, the native socket stream stores this option in the single sock->timeout field:

That timeout is used by both php_sockop_read() and php_sockop_write(). In particular, a blocking write which encounters EAGAIN/EWOULDBLOCK waits for POLLOUT using the same timeout:

This creates an ambiguity for extension and alternative stream-wrapper implementers: following the constant name and header comment produces a read-only implementation, while matching native PHP socket stream behavior requires applying the value to both blocking reads and blocking writes.

This ambiguity caused a real compatibility issue in Swoole's coroutine stream hook, where stream_set_timeout() changed the read timeout but a blocked fwrite() continued using the previous write timeout:

swoole/swoole-src#6260

The PHP manual currently says only that the function “sets the timeout value on the stream”; it does not document that native network/socket streams use the value for writes as well, and its example demonstrates only a read timeout:

https://github.com/php/doc-en/blob/master/reference/stream/functions/stream-set-timeout.xml

Suggested changes:

1. Clarify the stream_set_timeout() documentation: for native network/socket streams, the configured timeout applies to blocking reads and blocking writes.
2. Update the misleading comment in main/php_streams.h.
3. Introduce a direction-neutral internal name such as PHP_STREAM_OPTION_IO_TIMEOUT or PHP_STREAM_OPTION_TIMEOUT, while retaining PHP_STREAM_OPTION_READ_TIMEOUT as an alias for source compatibility, and migrate in-tree users to the clearer name.
4. Consider adding a php-src regression test covering a blocked socket-stream write after stream_set_timeout().

No runtime behavior change is being requested here; the goal is to make the existing behavior unambiguous and prevent downstream implementations from interpreting the option differently.