[WIP][DeepSeek] DeepSeek training and component integration with Titan main components

[lessw2020]

Mostly publishing for our status updates, but this PR:
a - starts integration of Deepseek training loop with Torch Titan main components
b - refactors deepseek modeling to start using Titan componenets such as .toml for model config and job config.
c - modularizes deepseek modeling overall.
d - moves all group_gemm components into kernels so that they can be leveraged by other models (including DSGemm)

[tianyu-l]

Maybe let's put this under deepseek folder, given its dependency on transformers. We can consider upstreaming it later.

[lessw2020]

sounds good - thanks for the feedback.

[tianyu-l]

Since this is only for MoE-based models, how about let's use https://github.com/pytorch/torchtitan/blob/main/docs/extension.md#extending-jobconfig
and create a separate .py config file in the deepseek folder. Later we can see if we can reuse them for Llama 4 and DeepSeek.