Chore: remove the sized bound on vector trait impl

[connortsui20]

Followup on #5197 because I forgot

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 84.87%. Comparing base (28f5b3d) to head (0ad94db).
⚠️ Report is 7 commits behind head on develop.

Files with missing lines	Patch %	Lines
vortex-vector/src/decimal/vector.rs	0.00%	1 Missing ⚠️

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