#0: Remove hardcoded grid width in all_gather and skip test_sharded_matmul test when the device grid size is too small

[tt-aho]

Ticket

Link to Github Issue

Problem description

All gather had hardcoded device width of 8 but should derive from device grid size.
Sharded MM unit test did not check if the shard config actually fits on the device grid.

What's changed

Change all gather to pull width from device.
Skip sharded MM test if device grid is too small.

Checklist

• Post commit CI passes
• Blackhole Post commit (if applicable)
• Model regression CI testing passes (if applicable)
• Device performance regression CI testing passes (if applicable)
• (For models and ops writers) Full new models tests passes
• New/Existing tests provide coverage for changes
  T3K unit: https://github.com/tenstorrent/tt-metal/actions/runs/12501718468
  T3K freq: https://github.com/tenstorrent/tt-metal/actions/runs/12506425069
  T3K nightly: https://github.com/tenstorrent/tt-metal/actions/runs/12506426406/job/34894919296
  T3K perf: https://github.com/tenstorrent/tt-metal/actions/runs/12506429619
  TG freq: https://github.com/tenstorrent/tt-metal/actions/runs/12506431709
  TG nightly: https://github.com/tenstorrent/tt-metal/actions/runs/12506432943

[SeanNijjar]

Thanks for the fix! Lgtm. You're going to also want to run TG frequent/nightly, t3k frequent, t4k and model perf.

[blozano-tt]

Thank you!