Add explicit `Extensions` type (#1062) #666

Job	Run time
draft (utoipa)	19s
draft (utoipa-gen)	9s
draft (utoipa-swagger-ui-vendored)	7s
draft (utoipa-swagger-ui)	7s
draft (utoipa-redoc)	6s
draft (utoipa-rapidoc)	5s
draft (utoipa-scalar)	10s
draft (utoipa-axum)	4s
draft (utoipa-config)	9s
	1m 16s

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