fix(websocket): bound slow-consumer output buffers

[loks0n]

Clients that stop reading can make Swoole retain enough outgoing data across connections to exhaust a realtime container. Port utopia-php/websocket#31 into the monorepo: default each connection's output buffer to 512KB, apply the limit to the listen port before startup, disable send_yield when capped, and disconnect clients when a push fails so message loss is not silent.

The constructor accepts socketBufferSize; passing 0 retains Swoole's default buffer size and yield behavior. Failed pushes still disconnect clients. The new default changes behavior for clients that fall behind, so this needs to be accounted for when choosing the release version.

Adds README guidance and an end-to-end regression that stops reading from one client, fills its outgoing buffer, and verifies that it is disconnected while another client still exchanges messages. This test fails both with the cap removed and with disconnect-on-failure removed.

Validation:

• bin/monorepo check websocket — Pint, PHPStan, and Rector pass.
• bin/monorepo test websocket — 9 unit tests and 3 end-to-end tests pass with real Swoole and Workerman servers.
• Both regression mutation checks fail at the expected stalled-client assertion; the restored implementation passes.
• bin/monorepo validate, Vale for the package README, and git diff --check pass.