Add filestream benchmarks for many files case, fix data race

[rdner]

Before it was only testing for a single file not the tests support many files.

During test runs with the race detector a data race was found and fixed.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
  - [ ] I have made corresponding changes to the documentation
  - [ ] I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
  - [ ] I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

This script will generate PDFs with CPU and memory profiles for each test case:

cd ./filebeat/input/filestream

go test -v -run=none -bench='BenchmarkFilestream/single_file/inode_throughput' -benchmem -benchtime=100x -cpuprofile=single-inode-cpu-profile.bin -memprofile=single-inode-mem-profile.bin
go tool pprof -pdf single-inode-cpu-profile.bin > single-inode-cpu-profile.pdf
go tool pprof -pdf single-inode-mem-profile.bin > single-inode-mem-profile.pdf

go test -v -run=none -bench='BenchmarkFilestream/single_file/fingerprint_throughput' -benchmem -benchtime=100x -cpuprofile=single-fp-cpu-profile.bin -memprofile=single-fp-mem-profile.bin
go tool pprof -pdf single-fp-cpu-profile.bin > single-fp-cpu-profile.pdf
go tool pprof -pdf single-fp-mem-profile.bin > single-fp-mem-profile.pdf

go test -v -run=none -bench='BenchmarkFilestream/many_files/inode_throughput' -benchmem -benchtime=10x -cpuprofile=many-inode-cpu-profile.bin -memprofile=many-inode-mem-profile.bin
go tool pprof -pdf many-inode-cpu-profile.bin > many-inode-cpu-profile.pdf
go tool pprof -pdf many-inode-mem-profile.bin > many-inode-mem-profile.pdf

go test -v -run=none -bench='BenchmarkFilestream/many_files/fingerprint_throughput' -benchmem -benchtime=10x -cpuprofile=many-fp-cpu-profile.bin -memprofile=many-fp-mem-profile.bin
go tool pprof -pdf many-fp-cpu-profile.bin > many-fp-cpu-profile.pdf
go tool pprof -pdf many-fp-mem-profile.bin > many-fp-mem-profile.pdf

many-fp-cpu-profile.pdf
many-fp-mem-profile.pdf
many-inode-cpu-profile.pdf
many-inode-mem-profile.pdf
single-fp-cpu-profile.pdf
single-fp-mem-profile.pdf
single-inode-cpu-profile.pdf
single-inode-mem-profile.pdf

Related issues

• Relates Add benchmark for filestream input #37317
• Relates Make filestream benchmark more precise and more re-usable #37334

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• Start Time: 2023-12-07T18:57:49.268+0000

• Duration: 133 min 27 sec

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Test	Results
Failed	0
Passed	8315
Skipped	755
Total	9070

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To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /package : Generate the packages and run the E2E tests.

• /beats-tester : Run the installation tests with beats-tester.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)