move split tests into test dir #505

Job	Run time
call / validate (ubuntu-latest, 3.12, validate)	2m 58s
call / tests (macos-latest, tests)	1m 38s
call / tests (windows-latest, tests)	2m 26s
call / checks (ubuntu-latest, 3.13)	1m 34s
call / checks (ubuntu-latest, 3.10)	1m 39s
call / checks (ubuntu-24.04, 3.11)	1m 38s
	11m 53s

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