benchmark creates new tokio runtime on every iteration

[hieuit095]

Description

The benchmark function b.iter(|| { let rt = Runtime::new().unwrap(); rt.block_on(...) }) creates a new Tokio runtime on every iteration. This is extremely expensive and will skew benchmark results significantly, causing measurements to include runtime creation overhead repeatedly.

Severity: medium
File: iroh-dns-server/benches/write.rs

Expected Behavior

The code should handle this case properly to avoid unexpected errors or degraded quality.