Add collectives configurations for different slice size

[hylin2002]

Summary

This PR introduces configurations for various Ironwood topologies (ranging from 2x2x1 to 4x4x4) and updates the time extraction logic for accurate benchmarking.

Key Changes

• New Topology Configurations: Added 3-in-1 configurations (all-gather, psum (all-reduce), and all-to-all) for multiple topologies in Ironwood/configs/collectives/.
• Updated Time Extraction Logic: Modified Ironwood/src/benchmark_utils.py to correctly accumulate execution time for split psum operations.

Reason for Logic Change

Previously, a single JAX psum operation generated two distinct HLOs (psum and ffi_call). The old logic treated these as two separate collective operations (e.g., if num_runs=5, it extracted 10 events).

This caused a ZeroDivisionError because the ffi_call completes in near 0ms. From a collectives perspective, these two HLOs represent a single logical step, so their execution times are now aggregated to prevent errors and ensure accurate timing.