feat: bench get_schedules_paginated and verify cursor monotonicity

[ekwe7]

Closes #777

Description

This PR adds performance benchmarks and correctness tests for RemittanceSplit::get_schedules_paginated, ensuring schedule pagination remains efficient and behaves correctly at scale.

Since schedule listing is frequently used by clients polling upcoming remittances, these additions help guarantee that gas consumption stays bounded as cursor positions advance and that pagination terminates without duplicates or missing entries.

Gas Benchmarks

• Added gas benchmarks for get_schedules_paginated with:

  • 1 schedule
  • 25 schedules
  • MAX_SCHEDULES_PER_OWNER (50 schedules)

• Verified that per-page gas cost remains bounded as the cursor advances.

Pagination Correctness Tests

Added tests to ensure:

• The union of all returned pages equals the complete schedule set.
• No schedules are duplicated or missed across pages.
• Pagination cursor strictly advances and eventually terminates.
• Returned schedules are ordered by ascending schedule ID.
• Requested limits are properly clamped.
• Schedules belonging to different owners remain isolated.

Edge Cases Covered

• Cursor positioned past the end of the schedule list.
• Single-schedule owners.
• Owners with exactly MAX_SCHEDULES_PER_OWNER schedules.

Documentation

• Updated SCHEDULE_GAS_BENCHMARKS_SUMMARY.md with benchmark results.

[Baskarayelu]

gas benchmarks plus a cursor-monotonicity check on get_schedules_paginated - exactly the kind of perf + correctness guard we want on the paginated query paths. merging 👍