chore: make fields in SerFunction private

Author: zjp-CN

src/functions/serialization.rs

@@ -5,17 +5,17 @@ use stable_mir::{CrateDef, DefId};
 #[derive(Debug, Serialize)]
 pub struct SerFunction {
     /// DefId in stable_mir.
-    pub def_id: String,
+    def_id: String,
     /// Every funtion must be declared in a specific file, even for those
     /// generated by macros.
-    pub file: String,
+    file: String,
     /// Attributes are attached the function, but it seems that attributes
     /// and function must be separated to query.
-    pub attrs: Vec<String>,
+    attrs: Vec<String>,
     /// Raw function string, including name, signature, and body.
-    pub func: String,
+    func: String,
     /// Recursive fnction calls inside the body.
-    pub callees: Vec<String>,
+    callees: Vec<String>,
 }
 
 impl SerFunction {