feat(cell): Add unit tests for GEMM.

[haruhi55]

This test for GEMM involves:

• [x] Loading a data tile from global memory to shared memory.
• [x] Chunking shared memory using the TileIterator.
• [x] Loading the data tile from shared memory to register.
• [x] Computing GEMM using Tensor Core's WMMA.
• [x] Storing the data tile from register to shared memory.
• [x] Storing the data tile from shared memory to global memory.
• [ ] pass unittest.

This PR relies on the prior merge of https://github.com/TiledTensor/TiledCUDA/pull/83.

[haruhi55]

close this pr and move it into a neat one.