This PR ports the core model into a Keras model and includes a weight conversion script.
VAE and rest of the pipeline would make sense in a separate PR.

Each layer is numerically compared against the original PyTorch implementation here: https://colab.research.google.com/drive/1TUI2outgEXA1-dczw4SU8i6z_7oj4CGu?usp=sharing

Modules included:

• Maths module
  • Timestep embedding
  • RoPE
  • Attention
  • Scaled dot product attention re-implementation in Keras (to match the PyTorch one)
• Layers module
  • MLPEmbedder
  • RMSNorm
  • QKNorm
  • SelfAttention
  • Modulation
  • DoubleStreamBlock
  • SingleStreamBlock
  • LastLayer