Remove using namespace std from testing tools, ossfuzz and yulPhaser

[hydai]

In this PR, I removed some of the using namespace std statements mentioned in #14403

• test/tools
• test/tools/ossfuzz
• tools/yulPhaser

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[nikola-matic]

Hey @hydai, thanks for this! The changes look good, however, you're missing a change to confirm that using namespace std was properly removed in scripts/check_style.

You'll need to add the following directories to the list:

test/tools/*
test/tools/ossfuzz/*
test/tools/ossfuzz/protomutators/*
tools/yulPhaser/*

Please add them and squash the commits into one, and we should be good to merge.

[hydai]

Hi @nikola-matic, I just added those folders into the scripts/check_style. Also, I modified the remaining files, so I changed the title to testing tools, ossfuzz and yulPhaser.