fix(bench): add missing diagnostics field in routing bench DispatchConfig

dispatch.rs:101 added a `diagnostics: bool` field to DispatchConfig
under #[serde(default)] but routing_benchmarks.rs:305 still constructs
the config with the old field set, breaking `cargo bench --no-run`.

Add `diagnostics: false` to match the field set.  Production callers
keep using DispatchConfig::default() so this only affects the bench.

Author: claude

benches/routing_benchmarks.rs

@@ -308,6 +308,7 @@ fn bench_dispatch_config_construction(c: &mut Criterion) {
                 track_axioms: true,
                 generate_certificates: true,
                 timeout: 60,
+                diagnostics: false,
             })
         })
     });