Add host API for alltoallmem_on_stream collective operation (#333)

* Add host-side rocshmem_alltoallmem_on_stream function

Function signature:
  rocshmem_alltoallmem_on_stream(rocshmem_team_t team, void *dest,
                                 const void *source, size_t size,
                                 hipStream_t stream)

- The function launches rocshmem_alltoallmem_kernel which calls
device-side alltoall<char> workgroup collective through default context.
- Uses dynamic block size determination via occupancy API.
- Implemented for all backends.

* Fix incorrect sync buffer size allocation for alltoall in GDA and IPC backends

When allocating memory for alltoall_pSync_pool in setup_teams() and
teams_init() functions, the code incorrectly used ROCSHMEM_BCAST_SYNC_SIZE
instead of ROCSHMEM_ALLTOALL_SYNC_SIZE.

* Add functional test for team_alltoallmem_on_stream

This commit adds a new functional test to verify the correctness of
the host-side rocshmem_team_alltoallmem_on_stream API.

* Add documentation for rocshmem_alltoallmem_on_stream

This commit adds API documentation for the host-side
rocshmem_alltoallmem_on_stream function in the collective routines
section. The documentation includes:

tests/functional_tests/tester.cpp

@@ -47,6 +47,7 @@
 #include "sync_all_tester.hpp"
 #include "team_sync_tester.hpp"
 #include "team_alltoall_tester.hpp"
+#include "team_alltoallmem_on_stream_tester.hpp"
 #include "team_barrier_tester.hpp"
 #include "team_broadcast_tester.hpp"
 #include "team_ctx_infra_tester.hpp"
@@ -227,6 +228,11 @@ std::vector<Tester*> Tester::create(TesterArguments args) {
       }
       testers.push_back(new TeamAlltoallTester<float>(args));
       return testers;
+    case TeamAlltoallmemOnStreamTestType:
+      if (rank == 0)
+        std::cout << "Alltoallmem_On_Stream ###" << std::endl;
+      testers.push_back(new TeamAlltoallmemOnStreamTester(args));
+      return testers;
     case TeamFCollectTestType:
       if (rank == 0) {
         std::cout << "Fcollect Test ###" << std::endl;
@@ -585,7 +591,8 @@ bool Tester::peLaunchesKernel() {
                 (_type == WAVESyncAllTestType) || (_type == WGSyncAllTestType) ||
                 (_type == RandomAccessTestType) || (_type == PingAllTestType) ||
                 (_type == TeamBarrierTestType) || (_type == TeamWAVEBarrierTestType) ||
-                (_type == TeamWGBarrierTestType);
+                (_type == TeamWGBarrierTestType) || 
+                (_type == TeamAlltoallmemOnStreamTestType);
 
   return is_launcher;
 }