Implement pytest tests for 06_message_passing examples

[Copilot]

This PR adds comprehensive pytest test coverage for the message passing examples in examples/06_message_passing/, following the established pattern from test_load_bench.py.

Overview

The implementation provides test coverage for both message passing examples:

• message_passing_load_store.py - Uses iris load/store operations for inter-rank communication
• message_passing_put.py - Uses iris put operations for inter-rank communication

Key Features

Comprehensive Test Coverage: The new test_message_passing.py provides 32 test combinations across:

• 4 data types: int8, fp16, bf16, fp32
• 2 buffer/heap size combinations: (4096, 1MB), (8192, 2MB)
• 2 block sizes: 512, 1024

Faithful Implementation: The tests exactly reproduce the validation logic from the original examples, ensuring that destination_buffer == source_buffer * 2 after the producer-consumer message passing operations complete.

Proper MPI Handling: Uses pytest.skip() to gracefully handle environments that don't have exactly 2 MPI ranks, which is required by the message passing examples.

Clean Architecture: Implements helper functions that mirror the original example structure:

• create_test_args() - Creates argument dictionaries matching the original parse_args() output
• run_message_passing_kernels() - Executes the core kernel logic without command-line argument parsing

Usage

# Run all message passing tests
pytest tests/examples/test_message_passing.py

# Run with MPI for actual execution
mpirun -np 2 python -m pytest tests/examples/test_message_passing.py

The tests follow the exact same pattern as the existing test_load_bench.py, using dynamic module imports via importlib.util and parameterized test functions for comprehensive coverage.

Fixes #60.

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