Fix: IsSortedKernel can return unknown, fix IsSorted for DictArray

[robert3005]

Signed-off-by: Robert Kruszewski github@robertk.io

[codspeed-hq]

CodSpeed Performance Report

Merging #4546 will improve performances by 10.68%

_{Comparing rk/issorted (2865fc1) with develop (d0e73e7)}

Summary

⚡ 2 improvements
✅ 1349 untouched benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	take_search[(0.005, 0.5)]	325.9 µs	294.7 µs	+10.57%
⚡	take_search[(0.005, 1.0)]	629.4 µs	568.6 µs	+10.68%

[codecov]

Codecov Report

❌ Patch coverage is 62.18487% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.59%. Comparing base (dbbd62f) to head (2865fc1).
⚠️ Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
...rtex-array/src/arrays/chunked/compute/is_sorted.rs	0.00%	12 Missing ⚠️
encodings/dict/src/compute/is_sorted.rs	0.00%	11 Missing ⚠️
vortex-array/src/arrays/bool/compute/is_sorted.rs	16.66%	10 Missing ⚠️
...ortex-array/src/arrays/varbin/compute/is_sorted.rs	0.00%	8 Missing ⚠️
encodings/runend/src/compute/is_sorted.rs	0.00%	2 Missing ⚠️
vortex-array/src/arrays/extension/compute/mod.rs	50.00%	1 Missing ⚠️
vortex-array/src/compute/is_sorted.rs	97.43%	1 Missing ⚠️

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