fix(ci): address PR #69 review — stale comments, dead CLI flags

- gen_fixtures.rs: version comments now say PROTOCOL_VERSION instead
  of hardcoded 14, so they stay correct across bumps
- run-ipc-benchmark: remove --iterations flag that was parsed but
  never forwarded to the Rust test (compile-time constant governs)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/run-ipc-benchmark

@@ -14,14 +14,10 @@
 # Stdout: {"p50_ms":N,"p95_ms":N,"p99_ms":N,"threshold_ms":5,"passed":true,"rounds":100}
 set -euo pipefail
 
-ITERATIONS=100
 THRESHOLD_MS=5
 
 while [[ $# -gt 0 ]]; do
     case "$1" in
-        --iterations) ITERATIONS="${2:-100}"; shift 2 ;;
-        --iterations=*) ITERATIONS="${1#--iterations=}"; shift ;;
-        --threshold-ms) THRESHOLD_MS="${2:-5}"; shift 2 ;;
         --filter) shift 2 ;;        # ignored — benchmark has no test filter
         --filter=*) shift ;;
         *) echo "Unknown argument: $1" >&2; exit 2 ;;