IPC ring bug impl with async read

EventFD class now expects the fd to already be init with open_eventfd
RingBuff Sender and Receiver fully manage SharedMemory and EventFD lifecycles, no aditional ctx mngrs needed
Separate ring buf tests into its own test bed
Add parametrization to test and cancellation
Add docstrings
Add simple testing data gen module .samples

@@ -0,0 +1,18 @@
+{ pkgs ? import <nixpkgs> {} }:

@@ -11,6 +14,7 @@ import tractor
 from tractor._shm import (
     open_shm_list,
     attach_shm_list,
+    EventFD, open_ringbuffer_sender, open_ringbuffer_receiver,

@@ -33,3 +34,3 @@
 )
 
-from msgspec import Struct
+from msgspec import Struct, to_builtins

@@ -833,1 +834,4 @@
     )
+
+
+if platform.system() == 'Linux':

@@ -834,0 +1030,4 @@
+            return self
+
+        async def __aexit__(self, exc_type, exc_value, traceback):
+            await self.aclose()

@@ -141,6 +141,7 @@ class ActorNursery:
         # a `._ria_nursery` since the dependent APIs have been
         # removed!
         nursery: trio.Nursery|None = None,
+        proc_kwargs: dict[str, any] = {}

@@ -834,0 +1123,4 @@
+            create=False
+        )
+        async with RingBuffReceiver(
+            shm, EventFD(fd=write_event_fd), EventFD(fd=wrap_event_fd, omode='w'), start_ptr=start_ptr

@@ -834,0 +914,4 @@
+    def close_eventfd(fd: int) -> int:
+        '''
+        Close the eventfd.
+        '''

@@ -834,0 +920,4 @@
+            raise OSError(errno.errorcode[ffi.errno], 'close failed')
+
+
+    class EventFD:

@@ -0,0 +216,4 @@
+        destaddr = destaddr or self._destaddr
+        assert isinstance(destaddr, tuple)
+
+        stream = await trio.open_tcp_stream(