Fix SageAttention naming and add strict precision control

- Renamed `sd2`/`sd3` to `sa2`/`sa3` across configuration, CLI, and ComfyUI nodes to fix naming confusion.
- Added strict `precision` control (`fp16`, `bf16`, `bf32`, `auto`) to CLI and internal configuration logic.
- Implemented robust fallback logic for SageAttention (SA3 -> SA2 -> Flash Attention 2 -> SDPA) with version checks.
- Updated `FP8CompatibleDiT` to exclude `FlashAttentionVarlen` modules from unnecessary wrapping.
- Added explicit logging ("🚀 Executing SageAttention...") to confirm kernel execution.
- Fixed bug where user-selected precision was being overridden by auto-detection defaults.
- Updated `src/interfaces/video_upscaler.py` to ensure precision setting is correctly propagated from ComfyUI node to generation context.

src/interfaces/video_upscaler.py

@@ -424,7 +424,8 @@ class SeedVR2VideoUpscaler(io.ComfyNode):
                 dit_offload_device=dit_offload_device,
                 vae_offload_device=vae_offload_device,
                 tensor_offload_device=tensor_offload_device,
-                debug=debug
+                debug=debug,
+                precision=precision
             )
 
             # Prepare runner with model state management and global cache