RUST-1743 Fix gridfs numeric type serialization (#941)

Author: abr-egn

src/gridfs.rs

@@ -31,6 +31,7 @@ pub(crate) struct Chunk<'a> {
     #[serde(rename = "_id")]
     id: ObjectId,
     files_id: Bson,
+    #[serde(serialize_with = "bson::serde_helpers::serialize_u32_as_i32")]
     n: u32,
     #[serde(borrow)]
     data: RawBinaryRef<'a>,
@@ -51,7 +52,10 @@ pub struct FilesCollectionDocument {
     pub length: u64,
 
     /// The size of the file's chunks in bytes.
-    #[serde(rename = "chunkSize")]
+    #[serde(
+        rename = "chunkSize",
+        serialize_with = "bson::serde_helpers::serialize_u32_as_i32"
+    )]
     pub chunk_size_bytes: u32,
 
     /// The time at which the file was uploaded.