Add fn read_header() to DatabaseStorage trait

bindings/javascript/src/lib.rs

@@ -473,6 +473,15 @@ impl DatabaseFile {
 }
 
 impl turso_core::DatabaseStorage for DatabaseFile {
+    fn read_header(&self, c: turso_core::Completion) -> turso_core::Result<turso_core::Completion> {
+        let r = c.as_read();
+        let size = r.buf().len();
+        assert!(
+            size == 100,
+            "the size of the database header must be 100 bytes, got {size}"
+        );
+        self.file.pread(0, c)
+    }
     fn read_page(
         &self,
         page_idx: usize,