feat(recurring): add pause/resume recurring payments

[AbdulmujibOladayo]

Summary

Adds pause_recurring and resume_recurring to allow a payer to temporarily halt charges without cancelling the recurring payment.

Changes

• Add paused: bool field to RecurringRecord (default false)
• Add pause_recurring(e, caller, recurring_id) — payer only, sets paused = true, emits recurring_paused event
• Add resume_recurring(e, caller, recurring_id) — payer only, sets paused = false, emits recurring_resumed event
• execute_recurring now checks !record.paused and panics if paused
• Expose both functions in contract.rs

closes #191

[drips-wave]

@AbdulmujibOladayo Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits