Sandbox: Enable mypy type checker #416

Job	Run time
Python 3.6 on ubuntu-20.04	34s
Python 3.7 on ubuntu-20.04	29s
Python 3.8 on ubuntu-20.04	22s
Python 3.9 on ubuntu-20.04	25s
Python 3.10 on ubuntu-20.04	22s
Python 3.11 on ubuntu-20.04	32s
Python 3.12 on ubuntu-20.04	26s
Python 3.13 on ubuntu-20.04	30s
Python pypy3.10 on ubuntu-20.04	1m 40s
Python 3.6 on macos-12	50s
Python 3.7 on macos-12	42s
Python 3.8 on macos-12	32s
Python 3.9 on macos-12	36s
Python 3.10 on macos-12	30s
Python 3.11 on macos-12	31s
Python 3.12 on macos-12	37s
Python 3.13 on macos-12	1m 5s
Python pypy3.10 on macos-12	1m 54s
Python 3.8 on macos-latest	52s
Python 3.9 on macos-latest	28s
Python 3.10 on macos-latest	22s
Python 3.11 on macos-latest	29s
Python 3.12 on macos-latest	24s
Python 3.13 on macos-latest	23s
Python pypy3.10 on macos-latest	1m 22s
Python 3.6 on windows-latest	1m 34s
Python 3.8 on windows-latest	1m 6s
Python 3.9 on windows-latest	41s
Python 3.10 on windows-latest	1m 13s
Python 3.11 on windows-latest	1m 19s
Python 3.12 on windows-latest	55s
Python 3.13 on windows-latest	1m 32s
Python pypy3.10 on windows-latest	6m 44s
	32m 1s

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