Move render-benchmarks under a Cargo feature (#3815)

## Summary

Avoid compiling these large dependencies when we typically don't need
them.

crates/uv-dev/src/render_benchmarks.rs

@@ -1,3 +1,5 @@
+#![cfg(feature = "render")]
+
 use std::path::{Path, PathBuf};
 
 use anyhow::{anyhow, Result};