Stop double-counting the _id field in DeveloperDocument::size() (#42663)

`DeveloperDocument.value` is a ConvexObject that already contains an `_id` field, no need to add the denormalized `id` field.

GitOrigin-RevId: 2f8d654552b0e4d80928fb03b3f64514d99e8d57

Author: goffrie

crates/common/src/document.rs

@@ -268,7 +268,7 @@ impl DeveloperDocument {
     }
 
     pub fn size(&self) -> usize {
-        self.id.size() + self.value.size()
+        self.value.size()
     }
 
     pub fn to_internal_json(&self) -> JsonValue {

crates/database/src/committer.rs

@@ -1021,13 +1021,12 @@ impl<RT: Runtime> Committer<RT> {
         }
         for validated_write in document_writes {
             let ValidatedDocumentWrite {
-                id: document_id,
                 write: DocumentWrite { document },
                 doc_in_vector_index,
                 ..
             } = validated_write;
             if let Some(document) = document {
-                let document_write_size = document_id.size() + document.size();
+                let document_write_size = document.size();
                 let tablet_id = document.id().tablet_id;
                 let Ok(table_namespace) = table_mapping.tablet_namespace(tablet_id) else {
                     continue;