Checking that MPI is installed before running QBC.

[mghibaudi]

Closes #78.

Rationale:

• The QBC application requires (and demonstrates) MPI usage. If users want to include it in the execution they need to install the MPI libraries for example via pip install QStone[mpi]

This PR raises an exception if users try to run QBC apps without MPI.

[Copilot]

Pull Request Overview

This PR adds MPI detection capability to the MPIHandler class and enforces MPI requirement for the QBC application. The changes introduce an isMPI() method that returns True for the real MPI implementation and False for the no-MPI mock implementation, and adds a check in QBC's initialization to ensure MPI support is available.

Key Changes

• Added isMPI() method to both MPI handler implementations to distinguish between real and mock MPI support
• Added MPI availability check in QBC application initialization that raises an ImportError when MPI is not available

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
qstone/multiprocessing/nompi.py	Adds isMPI() method returning False to indicate no MPI support
qstone/multiprocessing/mpi.py	Adds isMPI() method returning True to indicate real MPI support
qstone/apps/QBC.py	Adds MPI availability check in __init__ that raises error when MPI is unavailable

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