Add optional "precache" flag #311

Job	Run time
test_cache (ubuntu-latest)	12s
test_channel (ubuntu-latest, stable)	38s
test_cache (windows-latest)	2m 15s
lint_shellcheck	6s
test_channel (ubuntu-latest, beta)	44s
test_precache	25s
test_cache (macos-latest)	53s
test_channel (ubuntu-latest, master)	45s
test_cache (macos-13)	49s
test_channel (windows-latest, stable)	1m 39s
test_cache (macos-14)	31s
test_print_output	22s
test_channel (windows-latest, beta)	1m 40s
test_channel (windows-latest, master)	1m 29s
test_channel (macos-latest, stable)	1m 2s
test_channel (macos-latest, beta)	1m 14s
test_channel (macos-latest, master)	1m 17s
test_channel (macos-13, stable)	1m 31s
test_channel (macos-13, beta)	1m 29s
test_channel (macos-13, master)	1m 22s
test_channel (macos-14, stable)	42s
test_channel (macos-14, beta)	40s
test_channel (macos-14, master)	58s
test_channel (ubuntu-latest, main)	40s
	23m 23s

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