Check type hints with mypy #303

Job	Run time
system-testing (debian:testing-slim)	2m 34s
install (debian:bookworm-slim)	19s
system-testing (debian:unstable-slim)	2m 41s
skip-linters (debian:bookworm-slim)	23s
unittest (debian:bookworm-slim)	30s
install (debian:testing-slim)	21s
skip-linters (debian:testing-slim)	31s
system-testing (ubuntu:jammy)	3m 11s
skip-linters (debian:unstable-slim)	32s
unittest (debian:testing-slim)	27s
system-testing (ubuntu:noble)	3m 13s
skip-linters (ubuntu:jammy)	25s
system-testing (ubuntu:oracular)	2m 47s
install (debian:unstable-slim)	19s
unittest (debian:unstable-slim)	27s
skip-linters (ubuntu:noble)	31s
install (ubuntu:jammy)	29s
unittest (ubuntu:jammy)	28s
skip-linters (ubuntu:oracular)	26s
install (ubuntu:noble)	24s
unittest (ubuntu:noble)	30s
yamllint	11s
unittest (ubuntu:oracular)	34s
install (ubuntu:oracular)	28s
upload-to-codecov	8s
	22m 49s

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