Reuse MDBX cursors in static-file segment writers

[yongkangc]

Summary

• Reuse MDBX cursors in static-file segment writers to avoid per-block cursor setup.
• Keep walkers alive and reset ranges instead of reinitialising per block.

Motivation

When StaticFileProducer processes large block ranges it opens fresh read cursors for each block in transactions.rs and receipts.rs. Over millions of blocks this compounds into hundreds of thousands of cursor creations, extra allocations, and longer lock contention on MDBX. Reusing the cursor across the loop should cut CPU time and make writes faster for high throughput workloads.

References

• Tracking issue Tracking: DB Write Optimisation to Static Files #19057