return ShuttingDown error from registry instead of panic

Author: MarinPostma

libsql-wal/src/error.rs

@@ -17,6 +17,8 @@ pub enum Error {
     InvalidHeaderVersion,
     #[error("Invalid page size, only 4095 is supported")]
     InvalidPageSize,
+    #[error("Registry is shutting down")]
+    ShuttingDown,
 }
 
 impl Into<libsql_sys::ffi::Error> for Error {

libsql-wal/src/registry.rs

@@ -166,7 +166,7 @@ where
         namespace: &NamespaceName,
     ) -> Result<Arc<SharedWal<IO>>> {
         if self.shutdown.load(Ordering::SeqCst) {
-            todo!("open after shutdown");
+            return Err(crate::error::Error::ShuttingDown);
         }
 
         loop {