feat(contract): add deterministic expiry sweeping with bounded work

[arisu6804]

Problem

Expired records can remain fund-locking indefinitely, while unbounded sweeping can exceed transaction budgets.

Objective

Deliver a production-quality improvement to expired transfers, escrow records, and cleanup that creates measurable value for correctness, security, reliability, performance, or maintainability.

Implementation scope

• Define expiry timestamp semantics, permissionless or governed sweep behavior, bounded batch work, and idempotent cleanup.

Acceptance criteria

• Each eligible record is swept at most once; funds follow the documented expiry policy; a sweep never touches live transfers.

Required validation

• Boundary-time, repeated-sweep, batch-limit, authorization, and conservation tests.
• Existing tests and CI remain passing.
• Add regression coverage for the original failure mode.
• Do not weaken, delete, or skip unrelated tests to obtain a green build.

PR quality bar

• Keep the PR focused and explain design tradeoffs, compatibility impact, and test evidence.
• Avoid typo-only, documentation-only, cosmetic-only, or unrelated refactor submissions.

Out of scope

• Broad rewrites not required by the acceptance criteria.
• Changes to unrelated services, contracts, or user flows.

[Johnpii1]

hello
can i work on this pls

[grantfox-oss]

🦊 GrantFox — @Johnpii1 has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #189)
2. Your PR will be reviewed by the RemitFlow maintainers

Good luck! Track your progress on GrantFox.