feat: Reduce dependencies, especially with --no-default-features (#7)

* feat: Move unused dependencies to optional

* chore: Remove needless `once_cell` dependency

* `cargo make format`

Author: matheus23

Cargo.lock

@@ -28,24 +28,32 @@ unused-async = "warn"
 
 [dependencies]
 erased_set = "0.8"
-http-body-util = "0.1.0"
-hyper = { version = "1", features = ["server", "http1"] }
-hyper-util = { version = "0.1.1", features = ["tokio"] }
-once_cell = "1.17.0"
-prometheus-client = { version = "0.22", optional = true }
-reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }
 serde = { version = "1", features = ["derive"] }
 struct_iterable = "0.1"
 thiserror = "2.0.6"
-tokio = { version = "1", features = ["rt", "net", "fs"]}
 tracing = "0.1"
 
+# metrics feature
+http-body-util = { version = "0.1.0", optional = true }
+hyper = { version = "1", features = ["server", "http1"], optional = true }
+hyper-util = { version = "0.1.1", features = ["tokio"], optional = true }
+prometheus-client = { version = "0.22", optional = true }
+reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"], optional = true }
+tokio = { version = "1", features = ["rt", "net", "fs"], optional = true }
+
 [dev-dependencies]
 tokio = { version = "1", features = ["io-util", "sync", "rt", "net", "fs", "macros", "time", "test-util"] }
 
 [features]
 default = ["metrics"]
-metrics = ["prometheus-client"]
+metrics = [
+    "dep:http-body-util",
+    "dep:hyper",
+    "dep:hyper-util",
+    "dep:prometheus-client",
+    "dep:reqwest",
+    "dep:tokio",
+]
 
 [package.metadata.docs.rs]
 all-features = true

Cargo.toml

@@ -1,11 +1,12 @@
+use std::sync::OnceLock;
+
 use erased_set::ErasedSyncSet;
-use once_cell::sync::OnceCell;
 #[cfg(feature = "metrics")]
 use prometheus_client::{encoding::text::encode, registry::Registry};
 #[cfg(not(feature = "metrics"))]
 type Registry = ();
 
-static CORE: OnceCell<Core> = OnceCell::new();
+static CORE: OnceLock<Core> = OnceLock::new();
 
 /// Core is the base metrics struct.
 ///