Replace the col-major branch of `LayoutMatMulConfig::layout_matmul`
(which rejected rules 3-7) with a thin wrapper that delegates to the
row-major routine via the identity

    C[t, m, n] = A[t, m, k] @ B[t, k, n]   (row-major)
<=> C[n, m, t] = B[n, k, t] @ A[k, m, t]   (col-major)

i.e. reverse all axes and swap A/B. The returned layouts are reversed
and the A/B fields are swapped back so callers see the original operand
order.

This brings full broadcasting (rules 3-7) to col-major for free,
matching the convention that `DeviceMatMulAPI` impls already use
(see e.g. `device_faer/matmul.rs`, which reverses axes and swaps A/B
before dispatching to the row-major kernel).

Also:
- Update the module-level docs to describe the col-major convention
  (matmul dims are the first two; trailing dims broadcast).
- Replace the test that asserted col-major broadcasting fails with
  positive tests covering rules 3, 4 and 7 (incl. a `1` broadcast).
- Update the device_faer matmul test to exercise col-major broadcasting
  end-to-end via `set_default_order(ColMajor)`.

Co-authored-by: Claude Code <noreply@anthropic.com>
Co-authored-by: glm-5.1 <service@zhipuai.cn>