Follow-up cleanups to the merged AMD ROCm support PR #5301:
1. De-duplicate the torchao Windows-ROCm import stub into a single shared
module (studio/backend/core/_torchao_stub.py); both workers call one
install_torchao_windows_rocm_stub() entrypoint.
2. Align the gfx name/arch comment columns in setup.sh and setup.ps1.
3. Isolate the float16 dtype fallback to AMD without native bf16; NVIDIA
keeps dtype=None so unsloth's own bf16/fp16/FORCE_FLOAT32 detection is
honored.
4. Hoist unconditional stdlib imports (gc, glob, re, subprocess, copy,
types, sys, importlib.metadata) from function bodies to module top
across the PR #5301-touched files; heavy/optional/relative imports stay
lazy.
5. bitsandbytes Windows-ROCm install now uses plain pip (force_pip=True)
instead of UV_SKIP_WHEEL_FILENAME_CHECK, per the AMD hackathon docs.
Also adds scripts/verify_import_hoist.py (a scope-aware LEGB AST resolver
that catches dangling-alias and rename-clash bugs in import-hoist
refactors) and wires it into the Lint CI source-lint job as a self-test
plus a pull_request compare gate.
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