[tests] refactor c* pipeline tests. (#14626)

* refactor c* pipeline tests.

Migrate the remaining `tests/pipelines/` directories starting with C to the config class +
composable pytest mixins introduced in #14113: chroma, chronoedit, cogview3, consisid,
consistency_models, controlnet, controlnet_flux, controlnet_hunyuandit, controlnet_sd3 and
cosmos. cogvideo and cogview4 were already migrated.

Notable points beyond the mechanical conversion:

- Expected slices switch from the `"np"` layout (`[0, -3:, -3:, -1]`) to the `"pt"` one
  (`[0, -1, -3:, -3:]`); the values themselves are unchanged.
- The Cosmos `safety_checker` overrides (save/load, variants, dtype dict, encode_prompt)
  were duplicated across five files and now live in a shared
  `CosmosSafetyCheckerTesterMixin` in `tests/pipelines/cosmos/testing_utils.py`.
- chroma and controlnet_flux import `FluxIPAdapterTesterMixin` from `..flux.testing_utils`
  rather than the old `..test_pipelines_common` one.
- `PipelineTesterMixin.test_save_load_float16` now passes the non-deprecated `dtype=` to
  `from_pretrained` instead of `torch_dtype=`, which the Cosmos2.5 `from_pretrained`
  wrappers read when casting the safety checker they inject.
- Dropped along the way, matching #14619: `PipelineLatentTesterMixin`,
  `PipelineKarrasSchedulerTesterMixin`, the attention-slicing and xformers tests, and the
  `test_ip_adapter` overrides that only supplied an `expected_pipe_slice`.

`pytest tests/pipelines/{chroma,chronoedit,cogview3,consisid,consistency_models,controlnet,controlnet_flux,controlnet_hunyuandit,controlnet_sd3,cosmos}`
gives 14 failed, 1014 passed, 82 skipped. All 14 failures are in cosmos and reproduce
unchanged on main: `DummyCosmosSafetyChecker` is a parameter-less `ModelMixin` with a single
non-persistent buffer, so accelerate does not hook it for sequential offload and a reloaded
pipeline gets a fresh fp32 one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* fix

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>