Product updates: Multi-node training clusters, B200 and H200s, and Client 1.0 release

What this post added

Introduced multi-node training clusters with the `@clustered` decorator, enabling linear scaling of training runs across dozens of GPUs on multiple hosts via high-speed RDMA interconnect. Added support for NVIDIA B200 and H200 GPUs for serverless LLM inference, offering significant speedups over H100s. Released version 1.0 of the Modal client, emphasizing API stability and predictability, with specific updates including `modal.Volume.read_only`, `--secret` option for `modal shell`, timezone support for `Cron` schedules, and a `--timestamps` flag for `modal app logs`.