test: benchmark merging files in groups

[adamdecaf]

$ gotest . -bench BenchmarkMergeFiles -v -run BenchmarkMergeFiles -benchtime 10s goos: darwin
goarch: amd64
pkg: github.com/moov-io/ach
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkMergeFiles
BenchmarkMergeFiles/MergeFiles
    merge_bench_test.go:148: 1 files merged into 1 files
    merge_bench_test.go:148: 100 files merged into 40 files
    merge_bench_test.go:148: 10000 files merged into 4000 files
    merge_bench_test.go:148: 112369 files merged into 44949 files
BenchmarkMergeFiles/MergeFiles-16         	  112369	     96709 ns/op	    4220 B/op	     347 allocs/op
BenchmarkMergeFiles/MergeFiles_3Groups
    merge_bench_test.go:152: 1 files merged into 1 files
    merge_bench_test.go:152: 100 files merged into 55 files
    merge_bench_test.go:152: 10000 files merged into 6005 files
    merge_bench_test.go:152: 51914 files merged into 36354 files
BenchmarkMergeFiles/MergeFiles_3Groups-16 	   51914	    242804 ns/op	   11140 B/op	     897 allocs/op
BenchmarkMergeFiles/MergeFiles_5Groups
    merge_bench_test.go:155: 1 files merged into 1 files
    merge_bench_test.go:155: 100 files merged into 61 files
    merge_bench_test.go:155: 10000 files merged into 6079 files
    merge_bench_test.go:155: 53403 files merged into 34335 files
BenchmarkMergeFiles/MergeFiles_5Groups-16 	   53403	    231150 ns/op	   10625 B/op	     859 allocs/op
BenchmarkMergeFiles/MergeFiles_10Groups
    merge_bench_test.go:158: 1 files merged into 1 files
    merge_bench_test.go:158: 100 files merged into 61 files
    merge_bench_test.go:158: 10000 files merged into 6573 files
    merge_bench_test.go:158: 51963 files merged into 34870 files
BenchmarkMergeFiles/MergeFiles_10Groups-16         	   51963	    235732 ns/op	   10881 B/op	     878 allocs/op
BenchmarkMergeFiles/MergeFiles_100Groups
    merge_bench_test.go:161: 1 files merged into 1 files
    merge_bench_test.go:161: 100 files merged into 40 files
    merge_bench_test.go:161: 10000 files merged into 5923 files
    merge_bench_test.go:161: 53691 files merged into 34368 files
BenchmarkMergeFiles/MergeFiles_100Groups-16        	   53691	    229409 ns/op	   10596 B/op	     857 allocs/op
PASS
ok  	github.com/moov-io/ach	90.088s

[codecov-commenter]

Codecov Report

Merging #1282 (36bc682) into master (95c51d5) will not change coverage.
The diff coverage is n/a.

❗ Current head 36bc682 differs from pull request most recent head 1e47fe8. Consider uploading reports for the commit 1e47fe8 to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1282   +/-   ##
=======================================
  Coverage   88.58%   88.58%           
=======================================
  Files          73       73           
  Lines        7080     7080           
=======================================
  Hits         6272     6272           
  Misses        476      476           
  Partials      332      332