Restore producer-local FIFO ordering in bitmap mempool simulator

[will-break-it]

Problem

Bitmap-era block/EB assembly scanned global tx indices instead of producer-local arrival order, biasing inclusion toward earlier-index honest txs and distorting front-run fairness.

Fix

1. Keep bitmap membership/conflict checks, but restore producer-local arrival-order scanning for block and EB selection.
2. Ensure consume/diffuse cleanup removes tx and counterpart from both bitmaps and ordering state.
3. Add explicit rb_front_run_rate and total_front_run_rate, while keeping front_run_rate backward-compatible.
4. Standardize Praos/Leios processing schema and add stale/mixed-input guards in experiment scripts.
5. Add --no-eb-tx-cache to disable caching/gossip of EB-fetched txs into mempools when isolating EB backpressure effects.

Validation

• npm run --silent build
• npm test --silent
• Small 10-run smoke matrix (nodes=800, slots=200, adversaries 0/20/40/60/80, Praos + Leios) with slope/runtime summary.
• 30-run confidence rerun (3 repeats of the same matrix).