sycl-exp : dequant q4 k improvements

[AidanBeltonS]

This PR provides improvements to the dequantize_block_q4_K kernel. It focuses on improving the global memory accesses.

Three main changes are implemented:

• Single 32 bit load for half2 rather than two 16 bit loads
• Load all scales in to local memory then do random access on results
• Vectorize the q load so we load 32bits each time rather than 8bits

All results below collected on A100 GPU

		Without Changes	With Changes	% Change
LLama-bench 70 B	PP Throughput (t/s)	503.36	564.04	-11.85	Negative change is better
	NSYS Avg Kernel time (us)	587.54	409.52	30.30	Positive change is better

No meaningful change in Intel GPU results have been observed.

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[joeatodd]

Looks good, and I've tested it all locally 👍