Only require sync on FileAccessInterface when compiling for compare utilities.

Otherwise async compatibility would impact sync users of the plain library.

src/context/file_access_interface.rs

@@ -1,10 +1,16 @@
 use std::fmt::Debug;
 use std::path::PathBuf;
 
+#[cfg(any(feature = "compare", feature = "foreign_document_test"))]
 pub trait FileAccessInterface: Sync + Debug {
     fn read_file(&self, path: &str) -> Result<String, std::io::Error>;
 }
 
+#[cfg(not(any(feature = "compare", feature = "foreign_document_test")))]
+pub trait FileAccessInterface: Debug {
+    fn read_file(&self, path: &str) -> Result<String, std::io::Error>;
+}
+
 #[derive(Debug, Clone)]
 pub struct LocalFileAccessInterface {
     pub working_directory: Option<PathBuf>,