CUDA: use shared mem for ssm_conv

[am17an]

Add shared mem loading to ssm_conv_long_token for some mild benefit in prompt processing

At ub = 2048 on a 4090

Model	Test	t/s master	t/s cuda_ssm_conv	Speedup
qwen35 2B Q8_0	pp2048	27300.78	28136.03	1.03
qwen35 2B Q8_0	pp4096	26340.90	26944.11	1.02
qwen35 2B Q8_0	pp8192	25932.23	26401.70	1.02
qwen35 2B Q8_0	pp16384	24257.07	24673.20	1.02
qwen35moe ?B Q4_K_S	pp2048	6784.72	6872.92	1.01
qwen35moe ?B Q4_K_S	pp4096	6701.00	6810.24	1.02
qwen35moe ?B Q4_K_S	pp8192	6684.46	6787.67	1.02
qwen35moe ?B Q4_K_S	pp16384	6490.17	6578.51	1.01

[am17an]

Added some trivial fusions also

Model	Test	t/s 0141e9c	t/s cuda_ssm_conv	Speedup
qwen35 2B Q8_0	tg128	391.73	402.56	1.03
qwen35moe ?B Q4_K_S	tg128	183.79	186.81	1.02

[JohannesGaessler]

Do you intend to add still more features or is this ready for review?

[am17an]

This it it for now. Will add more in a separate PR

[IMbackK]

@am17an The hip compiler throws a bunch of warnings for this function because of this loop, tid is not known at compile time, obviously, so there is no way for the compiler to know how many iterations this loop should be unrolled to.

[IMbackK]

@ggerganov what do you think about -Werror for the hip build? the fact that the cuda compiler dosent warn for these cases has been a constant source of annoyance

[am17an]

oh right, I think this should be inside the loop like

for (int idx = 0; idx < total_elems; idx += split_d_inner) {
      int idx0 = idx0 + idx;
      ....
}

I think there are a lot of warnings we need to clean up before enabling -Werror, let me do that in separate PR

[IMbackK]

A least building the hip backend usually never throws any warnings we could restrict werror just to the hip objects and only for the ci build. or even just -werror for the transformation warning. The goal being that the failing hip backend on the ci run for a pr blocks this kind of thing from entering the codebase, which has happend alot.

[am17an]

Yes if this is the only warning for now, I'm okay enabling -Werror for HIP since it would help catch these bugs in the CI

[ggerganov]

@ggerganov what do you think about -Werror for the hip build?

@IMbackK Sounds good