Replace once_cell::OnceCell with std::sync::OnceLock. (#1246)

This PR removes the dependency on once_cell since all the relevant functionality is now in std.

Cargo.toml

@@ -39,7 +39,6 @@ jmespatch       = { version = "0.3", features = ["sync"], optional = true }
 kmip            = { version = "0.4.3", package = "kmip-protocol", features = [ "tls-with-openssl" ], optional = true }
 kvx             = { version = "0.9.3", features = ["macros"] }
 log             = "0.4"
-once_cell       = { version = "1.20.2", optional = true }
 openidconnect   = { version = "2.5.1", optional = true, default-features = false }
 openssl         = { version = "0.10", features = ["v110"] }
 oso             = { version = "0.12", optional = true, default-features = false }
@@ -76,7 +75,7 @@ syslog = "6.1.1"
 
 [features]
 default = ["multi-user", "hsm"]
-hsm = ["backoff", "kmip", "once_cell", "cryptoki", "r2d2"]
+hsm = ["backoff", "kmip", "cryptoki", "r2d2"]
 multi-user = [
     "basic-cookies",
     "jmespatch/sync",

src/commons/crypto/signing/signers/pkcs11/context.rs

@@ -35,7 +35,7 @@ use cryptoki::{
     slot::{Slot, SlotInfo, TokenInfo},
     types::AuthPin,
 };
-use once_cell::sync::OnceCell;
+use std::sync::OnceLock;
 
 use crate::commons::crypto::SignerError;
 
@@ -80,7 +80,7 @@ impl ThreadSafePkcs11Context {
 /// RwLock'd HashMap for this.
 type Pkcs11ContextsByFileName =
     Arc<RwLock<HashMap<String, ThreadSafePkcs11Context>>>;
-static CONTEXTS: OnceCell<Pkcs11ContextsByFileName> = OnceCell::new();
+static CONTEXTS: OnceLock<Pkcs11ContextsByFileName> = OnceLock::new();
 
 #[derive(Debug)]
 pub(super) struct Pkcs11Context {
@@ -106,14 +106,10 @@ impl Pkcs11Context {
     pub fn get_or_load(
         lib_path: &Path,
     ) -> Result<ThreadSafePkcs11Context, SignerError> {
-        // Initialize the singleton map of PKCS#11 contexts. Failure here
-        // should be impossible or else so severe that panicking is
-        // all we can do.
-        let contexts = CONTEXTS
-            .get_or_try_init(|| -> Result<Pkcs11ContextsByFileName, ()> {
-                Ok(Arc::new(RwLock::new(HashMap::new())))
-            })
-            .unwrap();
+        // Initialize the singleton map of PKCS#11 contexts.
+        let contexts = CONTEXTS.get_or_init(|| {
+            Arc::new(RwLock::new(HashMap::new()))
+        });
 
         // Use the file name of the library as the key into the map, if the
         // path represents a file.