Add handling of `.skip_lint` file(s) #227

Job	Run time
Setup as in PR for tools (3.11)	43s
Setup as in CI for tools (3.11)	3m 14s
Test testing of tools (0, 3.11)	3m 53s
Test linting of tools (3.11)	35s
Test testing of tools (1, 3.11)	3m 30s
Test testing of tools (2, 3.11)	3m 31s
Test combining 'chunked' test results (3.11)	35s
	16m 1s

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