Add convert_diffusers_to_cogvideox.py reverse conversion script

[Allure2233]

This script converts a HF Diffusers saved CogVideoX pipeline back to the original CogVideoX checkpoint format. It handles:

• Transformer: reverses key mappings (QKV merge, adaLN modulation merge, dense_4h_to_h, attention/mlp block renames)
• VAE: reverses key mappings (up_blocks index reversal, mid_block handling, resnets/block renames)
• Supports both safetensors and PyTorch (.bin) output formats
• Supports fp16/bf16 dtype casting

Closes #10076

What does this PR do?

Fixes # (issue)

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[Allure2233]

👋 @yiyixuxu @hlky — gentle ping, is there anything I can do to help move this forward? Happy to make any changes needed. Thanks!