Implement calc_on_order_fills execution

[luisleo526]

What changed

• implement opt-in historical calc_on_order_fills execution with a monotonic fill-event cursor
• cover standard bars and real lower-timeframe magnifier paths, including gap boundaries and durable stop-limit activation
• make ordinary process-on-close fills terminal while still processing all eligible close siblings
• expose generated-script checkpoint hooks for transactional fill recalculation

Why

The engine previously ignored calc_on_order_fills, so strategies could not recalculate after historical fills. That caused missing same-bar exits, stale next-bar brackets, incorrect reversal lifecycles, and excursion drift.

Validation

• focused calc-on-fill checks: 266/266
• full engine suite: 84/84
• margin/admission/default-quantity controls: 169/169, 72/72, 35/35
• corpus: 252/252; 239 excellent / 12 strong / 1 anomaly
• full immutable-TV sweep: 412 strategies, stable error inventory, 2 tier upgrades / 0 regressions
• protected TV, metrics, inputs, verifier, and tier key sets unchanged

Companion: pineforge-codegen-oss#53 supplies the generated checkpoint implementation.