Add rand-std feature

In test code imported from `rust-bitcoin` we feature gate on the
`rand-std` feature but forgot to add it. Recent compiler upgrade found
this for us.

Add a `rand-std` feature that enables `rand-std` in the `bitcoin`
dependency.

While we are at it add a `lints` section to the manifest.

Cargo.toml

@@ -20,6 +20,7 @@ rustdoc-args = ["--cfg", "docsrs"]
 default = ["std"]
 std = ["bitcoin/std"]
 no-std = ["bitcoin/no-std", "core2"]
+rand-std = ["bitcoin/rand-std"]
 serde = ["actual-serde", "bitcoin/serde"]
 base64 = ["bitcoin/base64"]
 
@@ -55,3 +56,6 @@ required-features = ["std"]
 [[example]]
 name = "v2-separate-creator-constructor"
 required-features = ["std"]
+
+[lints.rust]
+unexpected_cfgs = { level = "deny", check-cfg = ['cfg(rust_v_1_60)'] }

src/v0/bitcoin/mod.rs

@@ -1930,7 +1930,7 @@ mod tests {
         let secp = Secp256k1::new();
 
         let sk = SecretKey::new(&mut thread_rng());
-        let priv_key = PrivateKey::new(sk, crate::Network::Regtest);
+        let priv_key = PrivateKey::new(sk, bitcoin::Network::Regtest);
         let pk = PublicKey::from_private_key(&secp, &priv_key);
 
         (priv_key, pk, secp)