Improve performance by using Python C API to enter/exit context (#627)

* Optimize run_in_context calls
* Don't increase refcount in run_in_context since cython does it for us

Author: tarasko

uvloop/loop.pyx

@@ -92,31 +92,27 @@ cdef inline socket_dec_io_ref(sock):
 
 
 cdef inline run_in_context(context, method):
-    # This method is internally used to workaround a reference issue that in
-    # certain circumstances, inlined context.run() will not hold a reference to
-    # the given method instance, which - if deallocated - will cause segfault.
-    # See also: edgedb/edgedb#2222
-    Py_INCREF(method)
+    Context_Enter(context)
     try:
-        return context.run(method)
+        return method()
     finally:
-        Py_DECREF(method)
+        Context_Exit(context)
 
 
 cdef inline run_in_context1(context, method, arg):
-    Py_INCREF(method)
+    Context_Enter(context)
     try:
-        return context.run(method, arg)
+        return method(arg)
     finally:
-        Py_DECREF(method)
+        Context_Exit(context)
 
 
 cdef inline run_in_context2(context, method, arg1, arg2):
-    Py_INCREF(method)
+    Context_Enter(context)
     try:
-        return context.run(method, arg1, arg2)
+        return method(arg1, arg2)
     finally:
-        Py_DECREF(method)
+        Context_Exit(context)
 
 
 # Used for deprecation and removal of `loop.create_datagram_endpoint()`'s