fix(security): Add meta field to Tool struct in tests

Upstream changes to rmcp::model::Tool now require a meta field.
Updated test helper function create_test_tool to include meta: None.

Fixes compilation error after rebasing on updated main.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: surinderunitone

crates/agentgateway/src/mcp/security/native/tool_poisoning.rs

@@ -225,6 +225,7 @@ mod tests {
             description: description.map(|s| Cow::Owned(s.to_string())),
             icons: None,
             title: None,
+            meta: None,
             input_schema: Arc::new(
                 serde_json::from_value(serde_json::json!({"type": "object"}))
                     .unwrap()