* feat: Adjust RAM/VRAM calculation for unified memory systems
This commit refactors the logic for calculating **total RAM** and **total VRAM** in `is_model_supported` and `plan_model_load` commands, specifically targeting systems with **unified memory** (like modern macOS devices where the GPU list may be empty).
The changes are as follows:
* **Total RAM Calculation:** If no GPUs are detected (`sys_info.gpus.is_empty()` is true), **total RAM** is now set to $0$. This avoids confusing total system memory with dedicated GPU memory when planning model placement.
* **Total VRAM Calculation:** If no GPUs are detected, **total VRAM** is still calculated as the system's **total memory (RAM)**, as this shared memory acts as VRAM on unified memory architectures.
This adjustment improves the accuracy of memory availability checks and model planning on unified memory systems.
* fix: total usable memory in case there is no system vram reported
* chore: temporarily change to self-hosted runner mac
* ci: revert back to github hosted runner macos
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Co-authored-by: Louis <louis@jan.ai>
Co-authored-by: Minh141120 <minh.itptit@gmail.com>
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