vulkan: optimize conv2d and implement coopmat1 support (llama/22620)

vulkan: optimize conv2d and implement coopmat1 support (llama/22620)

* vulkan: add CONV_SHAPE_64x128 for medium-K conv2d

* vulkan: skip conv2d bounds checks when shapes align with tile sizes

* vulkan: use WG_SIZE=128 for CONV_SHAPE_64x32 conv2d

* vulkan: stage cm2 conv2d accumulator through shmem before global store

* vulkan: add coopmat1 conv2d path

* fallback when using too much shared memory. clean up comments

* Require 16x16x16 and subgroup size 32 or 64

* check whether shared memory is sufficient before overwriting conv2d params with coopmat1 values