Moved mscclpp_ncclGetUniqueId call into ncclCommInitRankFunc (#1332)

* Moved call to `mscclpp_ncclGetUniqueId` into `ncclCommInitRankFunc` to avoid setting up transport early in environments where MSCCL++ isn't valid.

* Checking `mscclEnabled` for the process and the topology to gate MSCCL++.

* Allowed `mscclForceEnable` to enable MSCCL++.

src/include/mscclpp/mscclpp_nccl.h

@@ -49,4 +49,6 @@ namespace std {
 
 bool operator ==(const ncclUniqueId& a, const ncclUniqueId& b);
 
+bool mscclppCommCompatible(ncclComm_t comm);
+
 #endif