Specs for chrono, cogview, flux2_klein, glm, hunyuandit, hyimage, joy,
kandinsky, longcat, nucleus, ovis, pixart and prx lived module-level in
model_<arch>.py. Move each into pipelines/<arch>/__init__.py to match
the layout used by anima, bria, ernie, f_lite, lens, qwen, step1x and
vibe.
Each model_<arch>.py now imports its spec lazily inside the load
function, so the package only gets pulled in when that arch is actually
loaded (kandinsky 2.x never goes through native dispatch and stays
untouched).
Also drop the "without this spec..." crash paragraph from the new
package docstrings plus ernie/__init__.py and bria/__init__.py.
ChronoEdit, HunyuanImage, Kandinsky5, LongCat, Ovis, NucleusMoE, Bria,
BriaFibo. Each inherits from_single_file via FromOriginalModelMixin
but has no SINGLE_FILE_LOADABLE_CLASSES entry; calling it crashed with
"FromOriginalModelMixin is currently only compatible with [...]".
TransformerSpec(cls=...) for each. Bria specs in
pipelines/bria/__init__.py; the rest are module-level in
model_<arch>.py since they have no package directory.