v0.8.0

• Introduced a new flexible and robust multi-backend mechanism and updated vendor adaptation methods.
• Enabled heterogeneous prefill-decoding disaggregation across vendor chips within a single instance via FlagCX (beta).
• Upgraded DeepSeek-v3 pre-training with the new Megatron-LM and added heterogeneous pre-training across different chips for MoE models like DeepSeek-v3.