Add gitignore file #1403

Job	Run time
ubuntu-24.04: /usr/bin/g++-14 Release PaRSEC	30m 24s
macos-latest: clang++ Release Pthreads	28m 29s
macos-latest: clang++ Debug PaRSEC	23m 16s
macos-latest: clang++ Debug Pthreads	24m 20s
ubuntu-24.04: /usr/bin/g++-14 Release Pthreads	30m 40s
ubuntu-24.04: /usr/bin/g++-14 Debug Pthreads	27m 10s
macos-latest: clang++ Release PaRSEC	22m 31s
ubuntu-24.04: /usr/bin/g++-14 Debug PaRSEC	25m 28s
	3h 32m 18s

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