style: wrap the cache-hints test imports to satisfy rustfmt

The Code Formatting job runs `cargo +nightly fmt --all -- --check`, and the
single-line `use rmcp::model::{...}` in this test exceeded the configured
width, failing the only red check on the PR. No behaviour change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: WAHIB-EL-KHADIRI <wahibelkhadiri06@gmail.com>

Author: WAHIB-EL-KHADIRI

crates/rmcp/tests/test_cache_hints.rs

@@ -1,4 +1,6 @@
-use rmcp::model::{CacheScope, ListToolsResult, ReadResourceResult, ResourceContents, ServerResult};
+use rmcp::model::{
+    CacheScope, ListToolsResult, ReadResourceResult, ResourceContents, ServerResult,
+};
 use serde_json::json;
 
 #[test]