build: use optional dependency syntax

The optional dependency syntax dep: ensures that the implicit features
of the optional dependencies are not created. This cleans up the library
interface for consumers, only our explicit flags are exposed.

Author: nyonson

Cargo.toml

@@ -42,8 +42,8 @@ tor-rtcompat = { version = "0.21.0", features = ["tokio"], optional = true }
 
 [features]
 default = ["database"]
-database = ["rusqlite"]
-tor = ["arti-client", "tor-rtcompat"]
+database = ["dep:rusqlite"]
+tor = ["dep:arti-client", "dep:tor-rtcompat"]
 filter-control = []
 
 [dev-dependencies]