Add experimental ggml-hexagon backend for the Hexagon NPU (llama/16547)

Add experimental ggml-hexagon backend for the Hexagon NPU (llama/16547)

* model: add support for extra bufs for all devices

* hexagon: add experimental ggml-hexagon backend for the Hexagon NPU

This commit introduces a new experimental backend `ggml-hexagon` with support for the Hexagon NPU.

Highlights:
- Supports Hexagon versions: v73, v75, v79, and v81
- Targets Android devices based on Snapdragon SoCs: Gen3, 8-Elite, and 8-Elite Gen5
- Supports Q4_0, Q8_0, MXFP4, and FP32 data types
- Implements core LLM ops: MUL_MAT/MUL_MAT_ID, ADD/SUB/MUL/ADD_ID, RMS_NORM, ROPE, GLU/SWIGLU, SOFTMAX

**Note:** This backend is experimental and may exhibit instability or limited performance across supported devices.
It is intended for early testing and feedback from llama.cpp/ggml developer and user community.

Co-Authored-By: Rajdeep Ganguly <redacted>
Co-Authored-By: Todor Boinovski <redacted>
* hexagon: fix format checker errors

* hexagon: update readme and cmake presets

* ci: add android-ndk-build jobs that build plain ARM64 and Snapdragon versions

* hexagon: add simple graph optimizer for stacking MUL_MAT ops with the same input

* hexagon: move ADB helper scripts into scripts/snapdragon/adb

* hexagon: replace all f/printfs with GGML_LOG_...

* readme: add hexagon to the list supported backends

* hexagon: stack malmuts with quantized inputs only

* hexagon: add TODO for fixing issues in hexagon_graph_optimize

* hexagon: update to hex-sdk 6.4.0 and add scripts for running on QDC

* scripts: fix lint errors

* scripts: update qdc pytest script to make linter happy

* hexagon: add reduce sum in fp32

* hexagon: reduce number of vector stores in matmul output

* hexagon: remove the need for vdelta in reduce-multiply-x8

* hexagon: consistent use of reduce_sum_fp32 for row_sums

* hexagon: some more matmul optimizations and comments

Optimize cases where tensor dims are not multiple of 1024 (e.g in Qwen models).
We've handled those cases already but at a higher overhead.

* hexagon: update cmake presets

* hexagon: add OPMASK support for run-bench.sh wrapper

* hexagon: update to use GGML_BACKEND_API

* hexagon: remove unused logic for setting tensor flags for the views

* hexagon: add asserts to set/get_tensor to make sure we handle complete tensors

Same asserts as the CPU backend.

* hexagon: use cpy_tensor slow path for non-host buffers

* hexagon: error checks in the buffer allocator

* cmake: move include(extProj) under ggml-hexagon

* hexagon: don't forget to delete the backend on free

* hexagon: set/get_tensor size assert apply only to quantized tensors

* hexagon: reintroduce HEX_VERBOSE wrapper for GGML_LOG_DEBUG for now

GGML_LOG_DEBUG is always enabled for test-backend-ops and the output gets in the way.
Ideally we need a bit more finer log levels.

* docs: typos in hexagon developer docs (libggm-...)

* hexagon: overhaul error handling in the session/device allocation

this should handle all failure paths in the session allocation.

* hexagon: update cmake presets to enable fp16 vectors

* hexagon: remove unused time_usec function

* hexagon: don't forget to release buffer contexts

* hexagon: fixed indents in hvx-utils (missed clang-format auto-format failure)

* hexagon: remove custom can_repeat function and use ggml_can_repeat

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Co-authored-by: Rajdeep Ganguly <redacted>
Co-authored-by: Todor Boinovski <redacted>