ci: Use reusable workflows for fmt and security_audit #607

Job	Run time
msrv (1.63)	49s
clippy	44s
test (ubuntu-latest, nightly)	57s
test (ubuntu-latest, beta)	58s
test (ubuntu-latest, stable)	58s
test (windows-latest, nightly)	2m 37s
test (windows-latest, beta)	2m 9s
test (windows-latest, stable)	3m 16s
test (macos-latest, nightly)	51s
test (macos-latest, beta)	47s
test (macos-latest, stable)	46s
fmt / fmt	12s
security_audit / security_audit	2m 46s
	17m 50s

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