Add read-update-write benchmark

Update the README with a new benchmark group and performance results.
Include new data files and update the Rust benchmark implementation.
Regenerate UPB bindings and fix a data path in the C benchmark runner.

benches/benches/hackers_bench.rs

@@ -27,7 +27,7 @@
 //! - `iterate`        — counting repeated fields at different nesting depths
 
 use criterion::{BenchmarkId, Criterion, Throughput, criterion_group, criterion_main};
-use roto_benches::hackers::{Campaign, Hacker, Operation, Worm};
+use roto_benches::hackers::{Campaign, CampaignBuilder, Hacker, Operation, Worm};
 use std::hint::black_box;
 
 // =============================================================================
@@ -223,9 +223,11 @@ fn bench_read_update_write(c: &mut Criterion) {
                 let mut buf = vec![0u8; data.len() * 2];
                 let res = CampaignBuilder::builder(&mut buf)
                     .name("updated")
+                    .unwrap()
                     .with(&campaign)
+                    .unwrap()
                     .finish();
-                black_box(res)
+                black_box(res.unwrap().len())
             })
         });
     }