fix: serialize TorchScript load/script behind a global lock

[grzegorz-roboflow]

What does this PR do?

torch.jit.load/script share a process-global, non-thread-safe registry; concurrent model loads (PINNED_MODELS preload) corrupt it. Thread an optional torchscript_state_global_lock through the SAM3/CLIP/YOLO loaders, always supplied by ModelManager, plus a regression test.

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Testing

test added

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in hard-to-understand areas
• My changes generate no new warnings or errors
• I have updated the documentation accordingly (if applicable)

Additional Context

N/A