feat: add BillingCacheService with 1-hour TTL for team subscription data

[devin-ai-integration]

What does this PR do?

This PR implements Redis-based caching for the BillingService using a proxy pattern, following reviewer feedback to remove the BillingCacheService abstraction. The implementation adds a 1-hour cache for billing subscription checks with proper cache invalidation when webhooks are received or cancelTeamSubscription is called.

Key Changes:

• ✅ Created IBillingService interface for type safety and dependency injection
• ✅ Implemented BillingServiceCachingProxy that directly uses RedisService
• ✅ Added cache invalidation for all Stripe webhook handlers and subscription cancellation
• ✅ Removed the unnecessary BillingCacheService abstraction layer
• ✅ Updated module configuration to use proxy pattern with DI
• ✅ Improved type safety with proper Prisma types in BillingData

Architecture: The proxy intercepts getBillingData() calls, checks Redis cache first, falls back to the underlying service on cache miss, and stores the result with 1-hour TTL. Cache is invalidated on billing-related events.

Visual Demo (For contributors especially)

N/A - This is an internal caching optimization with no user-facing changes.

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 caching optimization, no API changes.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

Environment Setup:

• Redis must be configured and running
• Stripe webhook endpoints should be configured

Test Scenarios:

1. Cache Hit/Miss: Call GET /v2/billing/{teamId}/check multiple times - first call should query database, subsequent calls should return cached data
2. Cache Invalidation: Trigger Stripe webhooks (subscription events, payment events) and verify cache is cleared
3. Subscription Cancellation: Call cancelTeamSubscription and verify cache is invalidated
4. Cache Expiry: Wait 1 hour and verify cache expires naturally

Expected Behavior:

• Billing data should be cached for 1 hour after first retrieval
• Cache should be immediately invalidated on relevant webhook events
• No functional changes to billing behavior, only performance improvement

Checklist

⚠️ Critical Review Areas:

• Cache invalidation logic - Verify all webhook handlers properly clear cache for correct team IDs
• Interface implementation - Ensure proxy correctly implements all IBillingService methods
• Redis error handling - Confirm service degrades gracefully if Redis is unavailable
• Type safety - Validate BillingData type matches actual service return types
• Cache key uniqueness - Verify cache keys are properly scoped by team ID

---

Link to Devin run: https://app.devin.ai/sessions/adaf284159974bde9c4695f62e310f87
Requested by: morgan@cal.com

This refactor addresses Keith's feedback to simplify the architecture by removing the intermediate BillingCacheService and having the proxy interact directly with Redis.

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2 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
cal	Ignored			Sep 23, 2025 7:50am
cal-eu	Ignored			Sep 23, 2025 7:50am

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E2E results are ready!

• Workflow #79617.1 latest results