[vulkan] Load F32 A matrix 2 at a time when its 2-aligned

[TheBlueMatt]

It turns out Intel doesn't particularly like loading F32s one at a time and we already have the _2aliagned load logic in mul_mat_vec, so here we use it.

While we do already check all the requirements to load elements 4 at a time across [B]F16 and F32, it turns out [B]F16 loading 4 at a time is sometimes slower on very specific shapes on Intel BMG. Loading 4 at a time is a bit faster on F32, but its not material and I assume might be slower on other platforms.

Note that we also need to validate a_offset is 2-aligned in mul_mat_vec.comp, which was missing in the original 2-way-load patch.

Some selected speedups from test-backend-ops perf on a B60 (obviously F32xF32 is pretty rare, but there are some steps that use it, so its nice to speed it up):

MUL_MAT(type_a=f32,type_b=f32,m=4096,n=1,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1704 runs - 767.17 us/run - 117.44 MFLOP/run - 153.08 GFLOPS
MUL_MAT(type_a=f32,type_b=f32,m=4096,n=1,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 2556 runs - 529.81 us/run - 117.44 MFLOP/run - 221.66 GFLOPS

MUL_MAT(type_a=f32,type_b=f32,m=4096,n=2,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1704 runs - 727.13 us/run - 234.88 MFLOP/run - 323.03 GFLOPS
MUL_MAT(type_a=f32,type_b=f32,m=4096,n=2,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 2130 runs - 528.84 us/run - 234.88 MFLOP/run - 444.15 GFLOPS

MUL_MAT(type_a=f32,type_b=f32,m=4096,n=3,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1704 runs - 702.19 us/run - 352.32 MFLOP/run - 501.74 GFLOPS
MUL_MAT(type_a=f32,type_b=f32,m=4096,n=3,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1988 runs - 532.14 us/run - 352.32 MFLOP/run - 662.08 GFLOPS

MUL_MAT(type_a=f32,type_b=f32,m=4096,n=4,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1278 runs - 919.50 us/run - 469.76 MFLOP/run - 510.89 GFLOPS
MUL_MAT(type_a=f32,type_b=f32,m=4096,n=4,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1917 runs - 543.69 us/run - 469.76 MFLOP/run - 864.03 GFLOPS

MUL_MAT(type_a=f32,type_b=f32,m=4096,n=5,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1197 runs - 892.12 us/run - 587.20 MFLOP/run - 658.21 GFLOPS
MUL_MAT(type_a=f32,type_b=f32,m=4096,n=5,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1881 runs - 575.17 us/run - 587.20 MFLOP/run - 1.02 TFLOPS

MUL_MAT(type_a=f32,type_b=f32,m=4096,n=8,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1498 runs - 716.40 us/run - 939.52 MFLOP/run - 1.31 TFLOPS
MUL_MAT(type_a=f32,type_b=f32,m=4096,n=8,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 1819 runs - 576.36 us/run - 939.52 MFLOP/run - 1.63 TFLOPS

MUL_MAT(type_a=f32,type_b=f32,m=4096,n=512,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 134 runs - 7467.09 us/run - 60.13 GFLOP/run - 8.05 TFLOPS
MUL_MAT(type_a=f32,type_b=f32,m=4096,n=512,k=14336,bs=[1,1],nr=[1,1],per=[0,1,2,3],k_v=0,o=1,src_overlap=0): 134 runs - 7478.12 us/run - 60.13 GFLOP/run - 8.04 TFLOPS

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• AI usage disclosure: NO (well, Qwen3.8-Flash-Next noted that this was worth doing, but I wrote the actual code here by hand).

[ggml-gh-bot]

Hi @TheBlueMatt, thanks for your contribution!

Per our contribution guidelines, the automated PR checker found the following issue(s) that need your attention:

• Multiple open PRs from a new contributor: We limit new contributors (those without a previously merged PR) to 1 open PR at a time. You currently have 2 open PRs.

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[TheBlueMatt]

bots buggy, I have 6 merged PRs...