Codegemma-7b-instruct failure on Metal

`cargo run --features metal --example gemma -- --which code-7b-it --prompt "explain isakmpd's architecture"`
fails with:
```
retrieved the files in 27.197292ms
loaded the model in 36.859128625s
explain isakmpd's architectureError: Metal error Invalid matmul arguments [1296, 81, 9, 1] [36864, 256, 4096, 1] (9, 256, 9)
```
The prompt is not of great importance, other prompts just give different strides, but fails equally.
I did look into this a bit, but I confess it sort of goes over my current competence. I thought the stride vector always should be decreasing, but the rhs stride info is, as can be seen [36864, 256, 4096, 1], which does not fit into my mental model. However the running with "--cpu" does accept this. I am still sceptic it does the math correctly, since it too seems to get the same striding, but it may be I that misunderstand the concept.

Start by reproducing the reported `cargo run --features metal --example gemma -- --which code-7b-it` command, then compare its Metal failure with the same invocation using `--cpu`. Trace the example's Metal matmul path and stride handling; done means the CodeGemma example accepts prompts on Metal without the reported invalid-matmul error.

Written by the indexing model from the issue text.