Add version metadata handling in merge command

Introduced logic to set the `version` field in resources during the merge process. The version is derived from the first resource's metadata or defaults to "1.0" if not present. This enhancement ensures compatibility with xcstrings format and improves overall resource metadata management alongside the existing `source_language` handling.

Author: WendellXY

langcodec-cli/src/merge.rs

@@ -83,10 +83,22 @@ pub fn run_merge_command(
 
             println!("Setting metadata.source_language to: {}", source_language);
 
+            // Set version field in the resources to make sure xcstrings format would not throw an error
+            let version = codec
+                .resources
+                .first()
+                .and_then(|r| r.metadata.custom.get("version").cloned())
+                .unwrap_or_else(|| "1.0".to_string());
+
+            println!("Setting metadata.version to: {}", version);
+
             codec.iter_mut().for_each(|r| {
                 r.metadata
                     .custom
                     .insert("source_language".to_string(), source_language.clone());
+                r.metadata
+                    .custom
+                    .insert("version".to_string(), version.clone());
             });
 
             if let Err(e) = converter::convert_resources_to_format(codec.resources, &output, format)