[quantization] Introduce wrapper for Qwen3VLVisionPatchMerger

[dvsav]

This change introduces QuantQwen3VLVisionPatchMerger wrapper to support post-training quantization of Qwen3VLVisionPatchMerger module.

Why?

Qwen3VLVisionPatchMerger module is used in the image encoder part of Qwen model.
Trying to quantize Qwen3VLVisionPatchMerger via PTQ generates exception PTQQuantizer: no quantization wrapper for Qwen3VLVisionPatchMerger.

What

This change introduces:

• Class QuantQwen3VLVisionPatchMerger (tico/quantization/wrapq/wrappers/qwen_vl/quant_vision_patch_merger.py).
• Unit tests: class TestQuantQwen3VLVisionPatchMerger (test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py) - skipped if transformers package is not installed.
• New entry tico.quantization.wrapq.wrappers.qwen_vl.quant_vision_patch_merger in _CORE_MODULES (tico/quantization/wrapq/wrappers/registry.py).
• Example of Qwen3VLVisionPatchMerger quantization and conversion to Circle (tico/quantization/wrapq/examples/qwen/quantize_qwen_vision_patch_merger.py).

Unit Tests

Unit tests results with coverage information:

$ coverage run -m pytest test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py -v
======================================================================================= test session starts ========================================================================================
platform linux -- Python 3.10.12, pytest-8.4.0, pluggy-1.6.0 -- /home/d.savchenkov/myenv/bin/python3
cachedir: .pytest_cache
rootdir: /home/d.savchenkov/TICO
configfile: pyproject.toml
plugins: anyio-4.12.0, mock-3.15.1, xdist-3.7.0, cov-6.2.1
collected 10 items                                                                                                                                                                                 

test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_activation_stats_collected PASSED                                        [ 10%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_different_batch_sizes      PASSED                                        [ 20%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_forward_diff               PASSED                                        [ 30%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_mode_transitions           PASSED                                        [ 40%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_module_override            PASSED                                        [ 50%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_observer_count             PASSED                                        [ 60%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_output_shape               PASSED                                        [ 70%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_registration_in_registry   PASSED                                        [ 80%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_subgraph_export            PASSED                                        [ 90%]
test/quantization/wrapq/wrappers/qwen_vl/test_quant_vision_patch_merger.py::TestQuantQwen3VLVisionPatchMerger::test_use_postshuffle_norm       PASSED                                        [100%]

================================================================================== 10 passed, 2 warnings in 8.50s ==================================================================================

Coverage info (irrelevant files skipped):

$ coverage report -m
Name                                                                   Stmts   Miss  Cover   Missing
----------------------------------------------------------------------------------------------------
...
tico/quantization/wrapq/wrappers/qwen_vl/quant_vision_patch_merger.py      45      0   100%
...
----------------------------------------------------------------------------------------------------
TOTAL                                                                   10274   4932    52%

[dvsav]

For Reviewers

Below is the source code of Qwen3VLVisionPatchMerger module that can be used to check the correctness of QuantQwen3VLVisionPatchMerger implementation:

# transformers/models/qwen3_vl/modeling_qwen3_vl.py

class Qwen3VLVisionPatchMerger(nn.Module):
    def __init__(self, config: Qwen3VLVisionConfig, use_postshuffle_norm=False) -> None:
        super().__init__()
        self.hidden_size = config.hidden_size * (config.spatial_merge_size**2)
        self.use_postshuffle_norm = use_postshuffle_norm
        self.norm = nn.LayerNorm(self.hidden_size if use_postshuffle_norm else config.hidden_size, eps=1e-6)
        self.linear_fc1 = nn.Linear(self.hidden_size, self.hidden_size)
        self.act_fn = nn.GELU()
        self.linear_fc2 = nn.Linear(self.hidden_size, config.out_hidden_size)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.norm(x.view(-1, self.hidden_size) if self.use_postshuffle_norm else x).view(-1, self.hidden_size)
        x = self.linear_fc2(self.act_fn(self.linear_fc1(x)))
        return x