[CORRUPTED] Synthetic Benchmark PR #26823 - fix: address proration implementation flaws

[ofir-frd]

Benchmark PR calcom#26823

Type: Corrupted (contains bugs)

Original PR Title: fix: address proration implementation flaws
Original PR Description: ## What does this PR do?

This PR addresses several flaws identified during code review of the custom proration implementation on the feat/proration branch:

1. Idempotency for Seat Tracking - Adds operationId field to SeatChangeLog model with a unique constraint to prevent duplicate seat change logs from race conditions when users flow through multiple code paths
2. Prevent Double Charging on Retry - Adds voidInvoice method that voids/deletes old invoices before creating new ones when retrying failed prorations
3. Due Date for Send Invoice - Adds daysUntilDue parameter (defaults to 30 days) for invoices using send_invoice collection method
4. Type Fix - Fixes type error in stripe-subscription-utils.ts (null to undefined conversion)

Link to Devin run: https://app.devin.ai/sessions/e1373fed6b8442b18a8344f6ae9c8353
Requested by: @sean-brydon

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. N/A - internal billing changes only.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

1. Idempotency: Call logSeatAddition or logSeatRemoval multiple times with the same operationId - should only create one record
2. Invoice Voiding: Trigger a failed proration retry and verify the old invoice is voided before creating a new one
3. Due Date: Create an invoice with send_invoice collection method and verify it has a 30-day due date

Note: The idempotency infrastructure is in place, but callers of logSeatAddition/logSeatRemoval will need to be updated to pass operationId values for the protection to be active.

Checklist for Human Review

• Verify Prisma migration is created for the new operationId field and unique constraint
• Review whether callers should be updated now to pass operationId values
• Check voidInvoice logic handles all invoice status edge cases appropriately
• Consider if unit tests should be added for the new functionality
  Original PR URL: fix: address proration implementation flaws calcom/cal.com#26823

Compliance Violation

• Rule: Custom Error Classes Must Use Hierarchical Structure with Typed Codes
• Language: TypeScript
• File: packages/features/ee/billing/service/proration/MonthlyProrationService.ts

[github-actions]

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 - revert: Reverts a previous commit

[github-actions]

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