feat: teach vortex-compact to compress decimal arrays

[danking]

For TPC-H, this brings the size from larger than Vortex standard to smaller.

Compressor	Size (GiB)	Size (btrblocks = 1.0)
btrblocks	2.9	1.00
compact (develop)	3.7	1.28
compact (this PR)	2.2	0.76

This has no effect on benchmarks run on my laptop.

I also avoided returning pco/zstd compressed arrays which were bigger than the uncompressed version. I saw this happen on some TPC-H columns. I suspec there's a real benefit to setting some size goal, like 90%, and storing uncompressed data unless we meet that goal.

[codspeed-hq]

CodSpeed Performance Report

Merging #4569 will not alter performance

_{Comparing dk/vx-compact-compresses-decimal (6ece637) with develop (60775e5)}

Summary

✅ 1351 untouched benchmarks

[codecov]

Codecov Report

❌ Patch coverage is 70.83333% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.57%. Comparing base (60775e5) to head (6ece637).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
vortex-layout/src/layouts/compact.rs	67.56%	12 Missing ⚠️
vortex-array/src/arrays/decimal/narrow.rs	81.81%	2 Missing ⚠️

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