Implement default RO context (#64)

* Allocate default context buffers and initialize queue for management

- Allocated the status flag, g return, and atomic return buffers for
  the default context.
- Initialized `AtomicWFQueueProxy` instances to manage these buffers
  efficiently for concurrent access.

* Update `BlockHandle` with default context buffers

* Add default context flag and update buffer retrieval functions

- Added a flag to distinguish the default context from other contexts.
- Modified return buffer functionns and `get_status_flag` function to accommodate
  the default context

* Add default context primitive tests

-  get, put, get_nbi, put_nbi, g, and p APIs.

src/reverse_offload/context_proxy.hpp

@@ -46,7 +46,7 @@ class DefaultContextProxy {
                                size_t num_elems = 1)
   : constructed_{true}, proxy_{num_elems} {
     auto ctx{proxy_.get()};
-    new (ctx) ROContext(reinterpret_cast<Backend*>(backend), -1);
+    new (ctx) ROContext(reinterpret_cast<Backend*>(backend), -1, true);
     rocshmem_ctx_t local{ctx, tinfo};
     set_internal_ctx(&local);
   }