use iterator for partition kernel instead of generating vec

[jimexist]

Which issue does this PR close?

based on #424
Closes #437

Rationale for this change

use iterator for partition kernel instead of generating vec

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #438 (e0f05a0) into master (0c00776) will decrease coverage by 0.00%.
The diff coverage is 92.50%.

❗ Current head e0f05a0 differs from pull request most recent head 9d11166. Consider uploading reports for the commit 9d11166 to get more accurate results

@@            Coverage Diff             @@
##           master     #438      +/-   ##
==========================================
- Coverage   82.71%   82.70%   -0.01%     
==========================================
  Files         163      163              
  Lines       44795    44791       -4     
==========================================
- Hits        37051    37045       -6     
- Misses       7744     7746       +2     

Impacted Files	Coverage Δ
arrow/src/compute/kernels/partition.rs	97.50% <92.50%> (-1.70%)	⬇️

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[alamb]

Looks like this PR needs a rebase.

[alamb]

Looks nice to me. 👍 @jimexist

[alamb]

FYI @jorgecarleitao