Improve build time of libcudf iterator tests

[davidwendt]

While working on #9641 I noticed that building the iterator gtests takes alot of time in CI. Here is a link to the individual build times for libcudf including the gtests:
https://gpuci.gpuopenanalytics.com/job/rapidsai/job/gpuci/job/cudf/job/prb/job/cudf-gpu-test/CUDA=11.5,GPU_LABEL=driver-495,LINUX_VER=ubuntu20.04,PYTHON=3.8/5173/testReport/(root)/BuildTime/
(you can sort by Duration by clicking on table colum header).

Here is a table of the top 20 compile time offenders as recorded on my local machine. Note that like the CI build output, 6 of the top 20 are just building the ITERATOR_TEST

rank	time (ms)	file
1	814334	/cudf.dir/src/search/search.cu.o
2	755375	/cudf.dir/src/sort/sort_column.cu.o
3	686235	/ITERATOR_TEST.dir/iterator/optional_iterator_test_numeric.cu.o
4	670587	/cudf.dir/src/groupby/sort/group_nunique.cu.o
5	585524	/cudf.dir/src/reductions/scan/scan_inclusive.cu.o
6	582677	/ITERATOR_TEST.dir/iterator/pair_iterator_test_numeric.cu.o
7	568418	/ITERATOR_TEST.dir/iterator/scalar_iterator_test.cu.o
8	563196	/cudf.dir/src/sort/sort.cu.o
9	548816	/ITERATOR_TEST.dir/iterator/value_iterator_test_numeric.cu.o
10	535315	/cudf.dir/src/groupby/sort/sort_helper.cu.o
11	531384	/cudf.dir/src/sort/is_sorted.cu.o
12	530382	/ITERATOR_TEST.dir/iterator/value_iterator_test_chrono.cu.o
13	525187	/cudf.dir/src/join/semi_join.cu.o
14	523726	/cudf.dir/src/rolling/rolling.cu.o
15	517909	/cudf.dir/src/reductions/product.cu.o
16	513119	/cudf.dir/src/stream_compaction/distinct_count.cu.o
17	512569	/ITERATOR_TEST.dir/iterator/optional_iterator_test_chrono.cu.o
18	508978	/cudf.dir/src/reductions/sum_of_squares.cu.o
19	508460	/cudf.dir/src/lists/drop_list_duplicates.cu.o
20	505247	/cudf.dir/src/reductions/sum.cu.o

I made some simple changes to the iterator code logic to use different thrust functions along with a temporary device vector. This approach improved the compile time of the ITERATOR_TEST by about 3x. Here are the results of compiling the above 6 files with the changes in this PR.

new rank	new time (ms)	file
59	232691 (2.9x)	optional_iterator_test_numeric.cu.o
26	416951 (1.4x)	pair_iterator_test_numeric.cu.o
92	165947 (3.4x)	scalar_iterator_test.cu.o
65	216364 (2.5x)	value_iterator_test_numeric.cu.o
77	186583 (2.8x)	value_iterator_test_chrono.cu.o
111	137789 (3.7x)	optional_iterator_test_chrono.cu.o

Total overall build time improved locally by ~3m (10%) using ninja -j48 install on a Dell 5820.

Here are the build time results of a CI build with these changes.
https://gpuci.gpuopenanalytics.com/job/rapidsai/job/gpuci/job/cudf/job/prb/job/cudf-gpu-test/CUDA=11.5,GPU_LABEL=driver-495,LINUX_VER=ubuntu20.04,PYTHON=3.8/5190/testReport/(root)/BuildTime/

[codecov]

Codecov Report

Merging #9788 (1055f21) into branch-22.02 (967a333) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@               Coverage Diff                @@
##           branch-22.02    #9788      +/-   ##
================================================
- Coverage         10.49%   10.47%   -0.02%     
================================================
  Files               119      119              
  Lines             20305    20341      +36     
================================================
  Hits               2130     2130              
- Misses            18175    18211      +36     

Impacted Files	Coverage Δ
python/cudf/cudf/__init__.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/column.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/frame.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/index.py	0.00% <ø> (ø)
python/cudf/cudf/core/indexed_frame.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/multiindex.py	0.00% <0.00%> (ø)
python/cudf/cudf/utils/utils.py	0.00% <0.00%> (ø)

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[davidwendt]

@gpucibot merge