Add native async I/O and an event loop with Fiber integratio

[TrixNEW]

Summary

zphp should provide a built-in async I/O runtime so PHP applications can handle large numbers of concurrent operations without blocking OS threads.

The event loop should use the best native backend available per platform, such as:

• epoll on Linux
• kqueue on macOS/BSD
• IOCP on Windows

It should integrate directly with PHP Fibers.

For example:

$data = await($socket->read());

Instead of blocking the thread, the current Fiber should suspend until the operation completes.

Initial scope

Support:

• TCP/UDP sockets
• timers
• DNS
• file descriptors/streams where practical
• cancellation
• timeouts
• wakeups
• Fiber suspension/resume

The runtime should avoid busy polling and unnecessary allocations.

Ideally there should be one reusable event-loop implementation that extensions and higher-level PHP libraries can build on.

Goals

• high concurrency with low thread count
• low idle CPU usage
• efficient native polling
• no blocking of unrelated Fibers
• clean cancellation/shutdown
• no leaks or dangling callbacks
• usable independently of zphp serve

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