CUDA: Improve NVFP4 W4A4 activation quantization (#25730)

CUDA: Improve NVFP4 W4A4 activation quantization (#25730)

* Squash history before conflict-resolution during rebase on master

WIP commit

Add 32-byte loads, restore per-block amax

Use nvfp4x4 intrinsic when available

Fuse per-channel amax and quantization kernels

Do pointer arithmetic only once on x

Remove unnecessary ternary in the load

We assert on host side that ne00 is 64-aligned

Add back scale-search, but optimize it with intrinsics

Code cleanup

Make scale in MMQ-epilogue NVFP4-specific/restrictive for now

Remove unneeded include, add comment

Fix trailing whitespace

Guard __builtin_align__(32) struct to NVIDIA

Seems like HIP doesn't have this available, see https://github.com/ggml-org/llama.cpp/actions/runs/29438651734/job/87431623001

* compiler massaging to avoid unnecessary LDCs

* kvalues_mxfp4 -> kvalues_nvfp4 in quantize_mmq_nvfp4

* Always pass in src1_scale.ptr

* Extract ggml_cuda_is_aligned helper