Feat: Add Wrappers for MPI_AllGatherv

[adit4443ya]

Towards #121

MPI_Allgatherv is similar to MPI_Gatherv, but instead of gathering data to a single root process, it gathers data to all processes in the communicator.

[gxyd]

Same concern I've with this PR as I mentioned in the other PR, i.e. we also need to make sure (by standalone tests) that the way the subroutine is used in pFUnit should be added as a standalone test case.

I see two uses of MPI_Allgather_v in pFUnit:

      call Mpi_allGatherV( &
           & values, size(values), MPI_INTEGER, &
           & global_list,   counts, displacements, MPI_INTEGER, &
           & this%mpiCommunicator, ier)

and the other is:

      call Mpi_AllgatherV( &
           & values_, size(values), MPI_LOGICAL, &
           & list,   counts, displacements, MPI_LOGICAL, &
           & this%mpiCommunicator, ier)

maybe we can ensure that we write test cases for different MPI_types and/or dimensions of array(s) (if any)

[gxyd]

I think we should've a utility function for this now, which should do this work for us now.

[adit4443ya]

Yes we can add utility function like we have for comm_world and other things. Will make a subsequent PR for that.

[adit4443ya]

Thanks for posting it's usecase in pFUnit. I will do this in evening!!(ASAP), for both PRs

[adit4443ya]

Why don't we do one thing,
when CI issue gets resolved then merge this PRs and then i will add respective tests for both subroutines MPI_Gatherv and MPI_Allgatherv.

As you mentioned the use case for them it includes the MPI_LOGICAL and MPI_CHARACTER datatype to be implemented which i would like to handle in separate PR.
so the flow would be

Get CI fixed -> merge pending PRs -> Add bindings with LOGICAL and CHARACTER -> Add pfUnit like tests for both subroutines (which will invlove to add subroutine which can take character arrays as an input ,currently it takes int/real(8) as input for sendbuf and recvbuf)

As doing all in these PRs would clutter things up
Let me know how that sounds.

[gxyd]

Get CI fixed -> merge pending PRs -> Add bindings with LOGICAL and CHARACTER -> Add pfUnit like tests for both subroutines (which will invlove to add subroutine which can take character arrays as an input ,currently it takes int/real(8) as input for sendbuf and recvbuf)

Yes, that's the idea. I just wanted you to be aware that I can't merge PR's for now, and any subsequent PR's might cause merge conflicts, which can be annoying sometimes.

[adit4443ya]

Now the CI are fixed, Should we merge pending PRs (there are 3 of them ) now? Need your approval

[gxyd]

Looks good to me, thanks @adit4443ya