Add IsNull expression to vortex-jni

[robert3005]

Add IsNull to vortex-jni bindings

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

[a10y]

Could you add this to the TestExpressionProtos suite just to make sure round-tripping works?

[codspeed-hq]

Merging this PR will improve performance by 29.94%

⚡ 2 improved benchmarks
✅ 1120 untouched benchmarks
⏩ 1530 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	take_10k_contiguous	314.9 µs	257 µs	+22.52%
⚡	Simulation	take_10k_random	251.2 µs	193.3 µs	+29.94%

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_{Comparing rk/jniisnotnull (aa348a6) with develop (8974afe)}

Footnotes

1. 1530 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩