Bloom filter optimizations (2/5): Eliminate lmem access during salt lookup in arrow policy

[sleeepyjack]

This PR is part 2/5 of the Bloom filter optimization project and must be merged in the correct order.

The arrow_filter_policy requires the lookup of a static salt from an array of length 8.
The current implementation lead to excessive local memory traffic induced by this lookup.
This PR fixes this by replacing the array lookup with an inline 8-way switch-case.

[mhaseeb123]

Looks good. Do we have any benchmarks that show the effect of this optimization?

[sleeepyjack]

@mhaseeb123 here they are

Benchmark results:

Ref=#669 Cmp=#670

arrow_bloom_filter_add_unique_size

[0] NVIDIA H100 80GB HBM3

Key	Distribution	NumInputs	FilterSizeMB	Ref Time	Ref Noise	Cmp Time	Cmp Noise	Diff	%Diff	Status
I64	UNIQUE	1000000000	1	85.883 ms	0.01%	43.649 ms	0.00%	-42233.580 us	-49.18%	FAST
I64	UNIQUE	1000000000	2	85.530 ms	0.01%	43.650 ms	0.00%	-41879.809 us	-48.97%	FAST
I64	UNIQUE	1000000000	4	85.575 ms	0.01%	43.650 ms	0.00%	-41924.872 us	-48.99%	FAST
I64	UNIQUE	1000000000	8	85.581 ms	0.01%	43.651 ms	0.00%	-41929.564 us	-48.99%	FAST
I64	UNIQUE	1000000000	16	85.665 ms	0.01%	43.653 ms	0.00%	-42012.336 us	-49.04%	FAST
I64	UNIQUE	1000000000	32	85.673 ms	0.01%	43.659 ms	0.00%	-42013.794 us	-49.04%	FAST
I64	UNIQUE	1000000000	64	85.723 ms	0.01%	51.861 ms	0.02%	-33862.236 us	-39.50%	FAST
I64	UNIQUE	1000000000	128	86.054 ms	0.01%	64.295 ms	0.00%	-21759.247 us	-25.29%	FAST

arrow_bloom_filter_contains_unique_size

[0] NVIDIA H100 80GB HBM3

Key	Distribution	NumInputs	FilterSizeMB	Ref Time	Ref Noise	Cmp Time	Cmp Noise	Diff	%Diff	Status
I64	UNIQUE	1000000000	1	11.330 ms	0.03%	11.373 ms	0.21%	43.710 us	0.39%	SLOW
I64	UNIQUE	1000000000	2	13.013 ms	0.14%	13.013 ms	0.07%	0.080 us	0.00%	SAME
I64	UNIQUE	1000000000	4	13.883 ms	0.13%	13.875 ms	0.02%	-7.219 us	-0.05%	FAST
I64	UNIQUE	1000000000	8	14.155 ms	0.24%	14.178 ms	0.02%	22.811 us	0.16%	SLOW
I64	UNIQUE	1000000000	16	14.326 ms	0.15%	14.335 ms	0.03%	8.940 us	0.06%	SLOW
I64	UNIQUE	1000000000	32	17.242 ms	0.11%	17.237 ms	0.06%	-5.357 us	-0.03%	SAME
I64	UNIQUE	1000000000	64	22.634 ms	0.20%	22.657 ms	0.14%	22.970 us	0.10%	SAME
I64	UNIQUE	1000000000	128	32.293 ms	0.15%	32.301 ms	0.06%	7.208 us	0.02%	SAME