[Examples] Add M=64 and multicta support in the test (#9584)

We allow M=64 and multicta layouts via multicast.

We also clean-up a few things from the example.

Given the current block-level semantics of `tmem_subslice` it's not
possible to have a `cga_layout = [[1, 0], [0, 1]]` as we would not be
able to split it along N.

Author: lezcano