MAX 26.3 release: Video generation & Mojo 1.0.0b1 type refinement

AI Impact Summary

The Modular 26.3 release introduces significant changes to MAX, notably adding video generation capabilities using Wan 2.1/2.2 diffusion models and expanding model support to include Gemma 4, Qwen3, and MiniMax-M2. Simultaneously, the Mojo 1.0.0b1 release focuses on type refinement and closure unification, aiming to simplify and improve the standard library. These changes require careful consideration for existing workflows, particularly regarding the deprecation of the `fn` keyword and the removal of negative indexing.