refactor(context-interface): deduplicate SSTORE refund sync in GasParams

[anim001k]

• deduplicate the sstore_set_refund / sstore_reset_refund synchronization in GasParams::new_spec_inner
• move the shared logic into a small private helper so refund slots stay aligned with the corresponding SSTORE cost slots
• keep behavior unchanged while reducing the chance of future drift when SSTORE gas values are updated

[codspeed-hq]

Merging this PR will not alter performance

✅ 176 untouched benchmarks

---

_{Comparing anim001k:patch-9 (23e9163) with main (3890cfa)}