Fix Gemma 4 NPU vision encoder on non-square images

[jakmro]

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[Copilot]

Pull request overview

This PR updates the Gemma 4 vision encoder NPU/CoreML export and runtime wiring so the vision encoder can accept additional runtime inputs (notably pixel_position_ids), enabling correct behavior on non-square images.

Changes:

• Export the vision encoder CoreML package with multiple named runtime inputs instead of a single x tensor.
• Add NPU runtime support for named multi-input inference with both FP16 and INT32 inputs, plus input-shape/introspection helpers.
• Avoid decoding full images in the tokenizer when only image dimensions are needed (via stbi_info wrapper).

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
python/cactus/transpile/npu/vision.py	Switches CoreML export to accept multiple named runtime inputs and defines CoreML input dtypes.
python/cactus/transpile/npu/pipeline.py	Routes vision encoder emission through the new multi-input export path and supports npu_module.
python/cactus/transpile/model_adapters.py	Introduces a Gemma4 vision encoder adapter variant for NPU export and configures runtime input count.
python/cactus/transpile/component_pipeline.py	Extends ComponentModuleSpec with NPU-specific module + runtime input count.
cactus-kernels/src/image.cpp	Adds cactus_image_info() wrapper over stbi_info.
cactus-kernels/cactus_kernels.h	Exposes cactus_image_info() in the public kernels header.
cactus-engine/src/tokenizer.cpp	Uses cactus_image_info() to compute Gemma4 image soft token counts without loading the full image.
cactus-engine/src/npu_ane.mm	Adds INT32 -> MLMultiArray copy support; exposes input presence/shape querying; supports dtype-aware multi-input feeding.
cactus-engine/src/npu_ane.h	Extends ANEEncoder interface for input presence/shape querying (and stubs for non-ANE builds).
cactus-engine/src/model.cpp	Passes pixel_position_ids into NPU vision encode for Gemma4.
cactus-engine/src/model_npu.cpp	Updates NPU vision encode to optionally send pixel_position_ids as INT32 named input.
cactus-engine/src/engine.h	Extends NPUNamedInput with dtype + void* data and adds NPU encoder input-introspection APIs.

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