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/collections/payments.ts

@@ -106,6 +106,15 @@ export function createPaymentsCollection(pluginConfig: BillingPluginConfig): Col
       hasMany: true,
       relationTo: extractSlug(pluginConfig.collections?.refunds || defaults.refundsCollection) as CollectionSlug,
     },
+    {
+      name: 'version',
+      type: 'number',
+      admin: {
+        hidden: true, // Hide from admin UI
+      },
+      defaultValue: 1,
+      required: true,
+    },
   ]
   if (overrides?.fields) {
     fields = overrides?.fields({defaultFields: fields})
@@ -129,6 +138,9 @@ export function createPaymentsCollection(pluginConfig: BillingPluginConfig): Col
       beforeChange: [
         async ({ data, operation, req }) => {
           if (operation === 'create') {
+            // Initialize version for new payments
+            data.version = 1
+
             // Validate amount format
             if (data.amount && !Number.isInteger(data.amount)) {
               throw new Error('Amount must be an integer (in cents)')
@@ -143,6 +155,15 @@ export function createPaymentsCollection(pluginConfig: BillingPluginConfig): Col
             }
 
             await initProviderPayment(req.payload, data)
+          } else if (operation === 'update') {
+            // Auto-increment version for updates (if not already set by optimistic locking)
+            if (!data.version) {
+              const currentDoc = await req.payload.findByID({
+                collection: extractSlug(pluginConfig.collections?.payments || defaults.paymentsCollection),
+                id: req.id as any
+              })
+              data.version = (currentDoc.version || 1) + 1
+            }
           }
         },
       ] satisfies CollectionBeforeChangeHook<Payment>[],