bench: Avoid tmp files in pwd #32890

It is a bit confusing that one bench run, when aborted, could leave behind temp files in the current working directory. It is similarly confusing to delete those files in the next run of bench.

Fix all issues by using BasicTestingSetup, which provides a proper temp folder to use and also cleans up after itself.

Can be tested via:

( echo 'my file content' > streams_tmp ) && ls streams_tmp && ./bld-cmake/bin/bench_bitcoin --filter=FindByte && ls streams_tmp

Previously the file would be deleted, now it is kept.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32890.

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ACK fa2fbaa4a29f80d3c7d5f0ad6b64035c3156dd12

Was able to reproduce both the pre- and post-fixed situation described, and can't find any other test instances that should be using the testing setup temp dir instead.