feat(core): refactor linters config and improve code quality (#119)

- [x] Reorganize golangci-lint configuration with documented disable reasons
- [x] Simplify errcheck and revive linter rules with targeted exclusions
- [x] Pre-compile regex patterns in input_validation.go for performance
- [x] Fix type assertions in memory_shard.go and resp.go with safety checks
- [x] Replace string comparison with EqualFold for case-insensitive matching
- [x] Fix loop variable captures in jwk.go and logout.go
- [x] Change high goroutine log level from Info to Debug in autocleanup.go
- [x] Replace deprecated "cancelled" spelling with "canceled" throughout
- [x] Add nolint annotations for intentional unused parameters
- [x] Improve comment formatting for deprecated functions
- [x] Fix comment spelling: "marshalling" → "marshaling"
- [x] Refactor provider warnings formatting in internal/providers/warnings.go
- [x] Simplify metrics summary building in internal/recovery/metrics.go
- [x] Pre-allocate slice in error_recovery.go GetDegradedServices
- [x] Refactor context cancellation checks in redis.go

internal/cache/backends/memory_shard.go

@@ -241,9 +241,11 @@ func (s *cacheShard) evictLRULocked() bool {
 
 	element := s.lruList.Back()
 	if element != nil {
-		item := element.Value.(*memoryCacheItem)
-		s.deleteItemLocked(item)
-		return true
+		item, ok := element.Value.(*memoryCacheItem)
+		if ok {
+			s.deleteItemLocked(item)
+			return true
+		}
 	}
 	return false
 }
@@ -267,8 +269,10 @@ func (s *cacheShard) getOldestAccessTime() time.Time {
 
 	element := s.lruList.Back()
 	if element != nil {
-		item := element.Value.(*memoryCacheItem)
-		return item.accessedAt
+		item, ok := element.Value.(*memoryCacheItem)
+		if ok {
+			return item.accessedAt
+		}
 	}
 	return time.Time{}
 }