Allow users to set UNSLOTH_STUDIO_HOME to relocate all studio data
(venvs, assets, outputs, exports, auth, cache, tensorboard runs).
Defaults to ~/.unsloth/studio when unset (no behaviour change).
Set HF_HOME, HF_HUB_CACHE, HF_XET_CACHE, UV_CACHE_DIR, and
VLLM_CACHE_ROOT to a unified location under ~/.unsloth/studio/cache/
on startup. This keeps all model downloads, datasets, and caches
in one place instead of scattered across ~/.cache/huggingface,
~/.cache/uv, etc.
Layout:
~/.unsloth/studio/cache/
huggingface/ (HF_HOME)
hub/ (HF_HUB_CACHE -- model/dataset downloads)
xet/ (HF_XET_CACHE -- xet blob store)
uv/ (UV_CACHE_DIR -- uv package cache)
vllm/ (VLLM_CACHE_ROOT -- vllm compiled kernels)
Only sets variables that are not already in the environment, so
user overrides (e.g. HF_HOME=/data/models) are respected.
Cross-platform: uses Path.home() which resolves correctly on
Linux (~), macOS (~), and Windows (C:\Users\<user>).
