Handle conditional NodeEntropy types for UniFFI

Adapt the NodeEntropy initialization to account for diverging
constructor signatures when the uniffi feature is active.

The UniFFI layer requires shared ownership (Arc) and dynamic byte
validation (Result/Vec) to facilitate memory management and error
handling across the FFI boundary. This change ensures the builder
receives the expected pointer type in UniFFI builds while
maintaining the zero-cost stack allocation for standard Rust usage.

Author: chuksys

tests/integration_tests_rust.rs

@@ -2445,6 +2445,9 @@ async fn persistence_backwards_compatibility() {
 
 	let storage_path = common::random_storage_path().to_str().unwrap().to_owned();
 	let seed_bytes = [42u8; 64];
+	#[cfg(feature = "uniffi")]
+	let node_entropy = Arc::new(NodeEntropy::from_seed_bytes(seed_bytes.to_vec()).unwrap());
+	#[cfg(not(feature = "uniffi"))]
 	let node_entropy = NodeEntropy::from_seed_bytes(seed_bytes);
 
 	// Setup a v0.6.2 `Node`