MPI function deprecation warning

```
SAMRAI_MPI.cpp:753:14: warning: 'MPI_Attr_get' is deprecated: MPI_Attr_get was deprecated in MPI-2.0; use MPI_Comm_get_attr instead [-Wdeprecated-declarations]
rval = MPI_Attr_get(d_comm, keyval, attribute_val, flag);
^
/usr/local/Cellar/open-mpi/5.0.1/include/mpi.h:3025:13: note: 'MPI_Attr_get' has been explicitly marked deprecated here
__mpi_interface_deprecated__("MPI_Attr_get was deprecated in MPI-2.0; use MPI_Comm_get_attr instead");
^
/usr/local/Cellar/open-mpi/5.0.1/include/mpi.h:302:78: note: expanded from macro '__mpi_interface_deprecated__'
# define __mpi_interface_deprecated__(msg) __attribute__((__deprecated__(msg)))
```

Start in SAMRAI_MPI.cpp at line 753 and inspect the deprecated MPI_Attr_get call alongside the compiler warning. Check the surrounding API usage and verify the build with Open MPI 5.0.1; done means the deprecated-function warning is no longer emitted.

Written by the indexing model from the issue text.