Switch Connection to use Arc instead of Rc

Connection needs to be Arc so that bindings can wrap it with `Mutex` for
multi-threading.

bindings/java/rs_src/limbo_connection.rs

@@ -8,19 +8,16 @@ use jni::objects::{JByteArray, JObject};
 use jni::sys::jlong;
 use jni::JNIEnv;
 use limbo_core::Connection;
-use std::rc::Rc;
 use std::sync::Arc;
 
 #[derive(Clone)]
 pub struct LimboConnection {
-    // Because java's LimboConnection is 1:1 mapped to limbo connection, we can use Rc
-    pub(crate) conn: Rc<Connection>,
-    // Because io is shared across multiple `LimboConnection`s, wrap it with Arc
+    pub(crate) conn: Arc<Connection>,
     pub(crate) io: Arc<dyn limbo_core::IO>,
 }
 
 impl LimboConnection {
-    pub fn new(conn: Rc<Connection>, io: Arc<dyn limbo_core::IO>) -> Self {
+    pub fn new(conn: Arc<Connection>, io: Arc<dyn limbo_core::IO>) -> Self {
         LimboConnection { conn, io }
     }