feat: Add deterministic inference pipeline for reproducible video generation

[q5sys]

Problem:
Running LTX-2 inference with identical inputs (same seed, prompt, settings) produced different video outputs between runs. This violated the expectation that a fixed seed should yield reproducible results.
See links below for example output proving this.

Root Cause:
Best I can tell, PyTorch and CUDA prioritize performance over bitwise determinism by default: scaled_dot_product_attention uses non-deterministic fused kernels, and cuBLAS may use non-deterministic algorithms.

Solution:
Added TI2VidTwoStagesPipelineDeterministic class with enable_deterministic_mode() that enforces reproducibility by:

• Setting torch.manual_seed() and CUDA seeds from the user-provided --seed
• Enabling torch.backends.cudnn.deterministic = True
• Disabling torch.backends.cudnn.benchmark
• Setting torch.use_deterministic_algorithms(True, warn_only=True)
• Configuring CUBLAS_WORKSPACE_CONFIG for deterministic matrix ops

Performance Impact (RTX 5090 benchmark):

	Original	Deterministic	Slowdown
Stage 1:	1.24 it/s	1.16 it/s	~6%
Stage 2:	1.18 s/it	1.22 s/it	~3%
Stage 3:	1.47 it/s	1.18 it/s	~20%

Overall ~1-2 seconds additional time for a ~27 second generation. The original TI2VidTwoStagesPipeline is preserved for users who prioritize speed.

I thought about making alterations to the original pipeline and enabling a --deterministic or --reproducible flag which would then enable this capability, but I figured it was safer and cleaner to just create a new pipeline since I'm not aware of what additional development you all have on your internal roadmap, and I wanted this to be as clean and simple for you to merge this into your existing development work.

Reference Files for PR: (See for scripts that were run and the output video)

With the Upstream Code:
Script: https://github.com/q5sys/hotdog-determinism/blob/main/run-ltx-hotdog.sh
Shell Log: https://github.com/q5sys/hotdog-determinism/blob/main/ltx-hotdog-shell-output.txt
Output 1: https://github.com/q5sys/hotdog-determinism/blob/main/hotdog-gpu0-1.mp4
Output 2: https://github.com/q5sys/hotdog-determinism/blob/main/hotdog-gpu0-2.mp4

With the Deterministic Pipeline:
Script: https://github.com/q5sys/hotdog-determinism/blob/main/run-ltx-hotdog-deterministic.sh
Shell Log: https://github.com/q5sys/hotdog-determinism/blob/main/ltx-hotdog-deterministic-shell-output.txt
Output 1: https://github.com/q5sys/hotdog-determinism/blob/main/hotdog-gpu0-deterministic-1.mp4
Output 2: https://github.com/q5sys/hotdog-determinism/blob/main/hotdog-gpu0-deterministic-2.mp4