fix(build): runtime hook to work around PyInstaller + Python 3.12 import breakages

Four distinct bundling-specific crashes blocked Kokoro and Qwen CustomVoice
from loading in the frozen binary:

1. torch._dynamo import triggered via class-body decorators
   (@torch._dynamo.allow_in_graph on PreTrainedModel,
   @torch.compiler.disable in flex_attention) pulls in torch._numpy._ufuncs
   which crashes on module load with NameError: name 'name' is not defined.

2. AlbertModel (Kokoro) triggers @auto_docstring -> modeling_auto ->
   GenerationMixin -> candidate_generator -> sklearn -> scipy, which hits
   the same class of bug in scipy.stats._distn_infrastructure (NameError:
   name 'obj' is not defined).

3. AutoModel (Qwen) pulls the same sklearn -> scipy chain directly.

4. librosa (required by most TTS engines) -> scipy.signal -> scipy.stats
   hits the _distn_infrastructure crash regardless of the transformers
   stubs above.

The root cause of (1) and (4) is that PyInstaller's frozen importer runs
module-level `for X in [<list-comp using dir()>]:` loops with an empty
iterable, leaving the loop variable unbound. Trailing `del obj` / unrelated
references then crash.

Fix: a single runtime hook (pyi_rth_torch_compiler_disable.py) installs:

- sys.modules stubs for torch._dynamo and torch._dynamo.config, plus a
  meta-path finder for torch._dynamo.* submodules — voicebox never uses
  torch.compile/dynamo for inference, so a permissive no-op stub (callable
  as decorator, falsey as predicate, context-manager-safe for
  TransformGetItemToIndex) is drop-in safe.
- meta-path finder stubs for transformers.utils.auto_docstring and
  transformers.generation.candidate_generator — both import-chain
  short-circuits; docstrings and speculative decoding aren't used for TTS.
- meta-path finder for scipy.stats._distn_infrastructure that reads the
  real .py source via the wrapped loader's get_source(), replaces the
  bundling-broken `del obj` with `globals().pop('obj', None)`, and
  compile+exec's the patched source. This keeps the real scipy module
  intact so librosa and everything downstream works normally.

Supporting changes:

- backend/pyi_hooks/hook-scipy.stats._distn_infrastructure.py sets
  module_collection_mode = "pyz+py" so the .py source is actually in the
  bundle for the runtime patcher to read.
- build_binary.py and voicebox-server.spec register the runtime hook and
  the new hooks dir.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

backend/pyi_hooks/hook-scipy.stats._distn_infrastructure.py

@@ -0,0 +1,12 @@
+"""
+Force scipy.stats._distn_infrastructure to be bundled with its .py source file
+alongside the .pyc bytecode.
+
+The runtime hook in backend/pyi_rth_torch_compiler_disable.py patches this
+module's source at load time (the module has a `del obj` at line 369 that
+raises NameError under PyInstaller's frozen importer). That patch reads the
+source via loader.get_source(), which only works if the .py file was
+actually collected into the bundle.
+"""
+
+module_collection_mode = "pyz+py"