chore: make workload_mix_realworld experiment params env-overridable (#396)

The performance test in workload_mix_realworld/run.sh hardcoded its
iteration count, batch size, and worker cap, so tuning a run required
editing the script (and produced noise diffs). Bind them from the
environment with the existing defaults as fallbacks:

  local -ir batch_size=${BATCH_SIZE:-1}
  local -ir total_iterations=${TOTAL_ITERATIONS:-10000}
  local -ir worker_max=${WORKER_MAX:-50}

Behavior is unchanged when the variables are unset. Example:
  WORKER_MAX=8 TOTAL_ITERATIONS=200 ./run.sh ...

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: bushidocodes

tests/workload_mix_realworld/run.sh

@@ -99,11 +99,12 @@ run_experiments() {
 	fi
 
 	# TODO: Check that workload is in spec.json
-	local -ir batch_size=1
+	# Experiment parameters, overridable via environment variables (defaults shown)
+	local -ir batch_size=${BATCH_SIZE:-1}
 	local -i batch_id=0
 	local -i roll=0
-	local -ir total_iterations=10000
-	local -ir worker_max=50
+	local -ir total_iterations=${TOTAL_ITERATIONS:-10000}
+	local -ir worker_max=${WORKER_MAX:-50}
 	local pids
 
 	printf "Running Experiments: "