fix: add optional timeout to McpClient::send_request() (#852)

We now impose a 10s timeout on the initial `tools/list` request to an
MCP server. We do not apply a timeout for other types of requests yet,
but we should start enforcing those, as well.

codex-rs/mcp-client/Cargo.toml

@@ -16,6 +16,7 @@ tokio = { version = "1", features = [
     "process",
     "rt-multi-thread",
     "sync",
+    "time",
 ] }
 
 [dev-dependencies]