ci: Use reusable workflows for fmt and security_audit #606

Job	Run time
msrv (1.63)	47s
clippy	43s
test (ubuntu-latest, nightly)	55s
test (ubuntu-latest, beta)	55s
test (ubuntu-latest, stable)	58s
test (windows-latest, nightly)	2m 22s
test (windows-latest, beta)	2m 2s
test (windows-latest, stable)	2m 46s
test (macos-latest, nightly)	55s
test (macos-latest, beta)	50s
test (macos-latest, stable)	47s
fmt / fmt	13s
security_audit / security_audit	2m 43s
	16m 56s

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