[adeebshihadeh]

Drops the Cython build dependency. The ipc and visionipc bindings are now handwritten C++ against the CPython limited API, so we ship one cp311-abi3 wheel per platform instead of one per Python version. A single wheel passes the full test suite on Python 3.11, 3.12, 3.13 and 3.14.

Same public API and module names (msgq.ipc_pyx, msgq.visionipc.visionipc_pyx).

Benchmark (in-process, ns/op, best of 3, pinned core)

	Cython (master)	this PR
send + recv, 64 B	2714	2621
send + recv, 1 KiB	2821	2740
send + poll + recv	2968	2751
receive(non_blocking=True), empty	56	21
all_readers_updated()	19	17

Cross-process 1 KiB ping-pong is within noise (~145–150k msgs/s for both). The stripped .so is about half the size, and ipc builds in ~1 s instead of ~5 s (cythonize + compile).

Small behavior changes

• Poller.poll() returns the registered SubSocket objects instead of new non-owning wrappers
• PubSocket.send() accepts any buffer, not only bytes
• Event.wait(), wait_for_one_event(), VisionIpcClient.connect() and available_streams() release the GIL while blocking; non-blocking receive no longer does
• VisionBuf keeps its client alive and can't be instantiated directly
• .pxd files are no longer shipped, so cimport from msgq is no longer possible