[serge] Fix 10 integration tests for model `gemma3` failing with `output_mismatch` (list output differs (8), other (2))
Author: sergereview[bot]
Pull request: yes

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## Original CI failure

- Failure group: `1/1: 10 integration tests for model `gemma3` failing with `output_mismatch` (list output differs (8), other (2))`
- `tests/models/gemma3/test_modeling_gemma3.py::Gemma3IntegrationTest::test_dynamic_sliding_window_is_default` [multi-gpu] (output_mismatch, seen 6/7)

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Relates to #47309

Fixes the `test_dynamic_sliding_window_is_default` failures in the Gemma3 integration group. The generation code from #40039 unsets `cache_implementation="hybrid"` so that models with sliding-window attention use the dynamic sliding-window cache by default. It was unsetting this value unconditionally, so an explicit `cache_implementation="hybrid"` passed to `generate()` was ignored and a `DynamicCache` containing `DynamicSlidingWindowLayer` layers was returned instead of the static hybrid cache.

The patch only unsets `"hybrid"` when it was not explicitly provided in `generate()` kwargs, preserving user intent.

Note: The normalizer failures (`modeling_rules_doc`, `docstrings`) are caused by a missing `transformers.models.tipsv2` module / `Tipsv2Config` import, which is unrelated to this change.

---
_This change was produced automatically by serge from a CI failure report. The patch was generated by an LLM and applied by serge; review before merging._

_serge `v0.1.0` · model: `moonshotai/Kimi-K2.7-Code` · 62 LLM turns · 62 tool calls · 194.5s · 2151228 in / 20968 out tokens_

Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_47310). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

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### CI recap

**Dashboard:** [View test results in Grafana](https://transformers-ci.lor-e.huggingface.cool/d/pytest-observability-by-pr/pytest-observability-branch?var-pr=47310)
**Latest run:** [29297459387:1](https://github.com/huggingface/transformers/actions/runs/29297459387)
**Result:** `success` | **Jobs:** 15 | **Tests:** 171,053 | **Failures:** 0 | **Duration:** 14h 20m

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run-slow: gemma3

[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/29411689151)

This comment contains `run-slow`, running the specified jobs: 

models: ["models/gemma3"]
quantizations: []

## CI Results
[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/29411689151)

### Commit Info
| Context | Commit | Description |
|---------|--------|-------------|
| RUN | [2ab07868](https://github.com/huggingface/transformers/commit/2ab078686ca2ef4a7eb1d8bf091276dc1363df71) | workflow commit (merge commit) |
| PR | [c02bfb6c](https://github.com/huggingface/transformers/commit/c02bfb6c2836ef1f3acb6aaa9bc71feb29d09900) | branch commit (from PR) |
| main | [e194978a](https://github.com/huggingface/transformers/commit/e194978ab2043fe57150aafea53a4efbea77258c) | base commit (on `main`) |

⚠️ **Model CI failed to report results**

The test failure analysis could not be completed. Please check the [workflow run](https://github.com/huggingface/transformers/actions/runs/29411689151) for details.