Wrap extension schema version in a newtype (#9872)

This PR wraps the extension schema version in a newtype, for some
additional type safety.

Release Notes:

- N/A

crates/extension_cli/src/main.rs

@@ -95,7 +95,7 @@ async fn main() -> Result<()> {
         version: manifest.version,
         description: manifest.description,
         authors: manifest.authors,
-        schema_version: Some(manifest.schema_version),
+        schema_version: Some(manifest.schema_version.0),
         repository: manifest
             .repository
             .ok_or_else(|| anyhow!("missing repository in extension manifest"))?,