fix: Implement true atomic optimistic locking and enhance type safety

🔒 Critical Race Condition Fixes:
- Add version field to payment schema for atomic updates
- Implement true optimistic locking using PayloadCMS updateMany with version checks
- Eliminate race condition window between conflict check and update
- Auto-increment version in beforeChange hooks

🛡️ Type Safety Improvements:
- Replace 'any' type with proper ProviderData<T> generic
- Maintain type safety throughout payment provider operations
- Enhanced intellisense and compile-time error detection

⚡ Performance & Reliability:
- Atomic version-based locking prevents lost updates
- Proper conflict detection with detailed logging
- Graceful handling of concurrent modifications
- Version field hidden from admin UI but tracked internally

🔧 Configuration Validation:
- All critical validation moved to provider initialization
- Early failure detection prevents runtime issues
- Clear error messages for configuration problems

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/plugin/types/payments.ts

@@ -48,6 +48,7 @@ export interface Payment {
     | boolean
     | null;
   refunds?: (number | Refund)[] | null;
+  version: number;
   updatedAt: string;
   createdAt: string;
 }