fix: actually load SoVITS weights in CLI and GUI entrypoints

[kyo-zzz]

Problem

inference_cli.py and inference_gui.py call change_sovits_weights() as a plain statement. That function is a generator (it yields Gradio UI-update dicts for the webui), so calling it only creates a generator object: the body never runs. As a result --sovits_model is silently ignored — change_gpt_weights() works because it is a regular function, which is exactly the asymmetry that makes this easy to miss. Audio still gets produced because inference_webui loads the default v2 model at import time (its own next(...) call, wrapped in a bare try/except), so the CLI synthesizes with whatever model was loaded at startup instead of the one the user asked for.

Fixes #2829.

What changed

1. inference_cli.py / inference_gui.py — iterate the generator (for _ in change_sovits_weights(...): pass) so the SoVITS weights actually load and load errors surface.
2. inference_webui.py — consuming the generator end-to-end exposed a second latent bug: the post-load yield references six locals (prompt_text_update, prompt_language_update, text_update, text_language_update, visible_sample_steps, visible_inp_refs) that were only assigned when the webui passes UI language args. Any arg-less call therefore raised UnboundLocalError at that yield — invisible until now because the import-time next() swallows everything with except: pass. These six locals now get neutral defaults ({"__type__": "update"} / False); the webui path overwrites all of them exactly as before.

Verification

Windows 11, CPU only (torch 2.5.1+cpu), v2 pretrained models (s1bert25hz-5kh-longer-epoch=12-step=369668.ckpt + s2G2333k.pth):

• Before the fix (reproduces inference_cli.py never loads the SoVITS model: change_sovits_weights is a generator and is called without being iterated #2829): inference_cli.py --sovits_model NONEXISTENT_BOGUS.pth → exit 0, output.wav produced, using the silently-wrong default model. No error anywhere.
• After the fix, bogus path: exit 1 with FileNotFoundError: [Errno 2] No such file or directory: 'NONEXISTENT_BOGUS.pth' — fails fast instead of silently synthesizing with the wrong model.
• After the fix, valid path: exit 0, output.wav produced, and the log shows loading sovits_v2 <All keys matched successfully> twice (import-time load + the CLI's own call) with the requested path echoed by the function's own print — the requested model actually loads.
• Webui path regression: calling change_sovits_weights(sovits_path, prompt_language="中文", text_language="中文") and consuming the generator yields exactly 2 events, the button goes disabled → interactive, and the 4th update dict carries value == "中文" from the argument — gradio behavior unchanged.
• ruff check on the three touched files reports the same 62 pre-existing findings before and after the change (none in the added lines); ruff format --diff output is identical to the pristine file's (all pre-existing).

Note

The GUI call site gets the identical fix; I verified it by code-path identity (same function, same consumption pattern, same arg-less signature) — the runtime evidence above comes from the CLI, which shares the entire loading path.