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{}
 }

internal/cache/backends/redis.go

@@ -345,7 +345,7 @@ func (r *RedisBackend) prefixKey(key string) string {
 
 // executeWithRetry executes a Redis operation with exponential backoff retry logic.
 // It checks context cancellation at multiple points to ensure fast abort when the
-// caller's context is cancelled (e.g., due to request timeout).
+// caller's context is canceled (e.g., due to request timeout).
 func (r *RedisBackend) executeWithRetry(ctx context.Context, operation func(*RedisConn) error) error {
 	maxRetries := 3
 	baseDelay := 50 * time.Millisecond // Reduced from 100ms to fail faster
@@ -377,7 +377,7 @@ func (r *RedisBackend) executeWithRetry(ctx context.Context, operation func(*Red
 		err = operation(conn)
 		r.pool.Put(conn)
 
-		// Check context after operation - if cancelled, don't bother retrying
+		// Check context after operation - if canceled, don't bother retrying
 		if ctx.Err() != nil {
 			return ctx.Err()
 		}

internal/cache/backends/redis_pool_test.go

@@ -201,7 +201,7 @@ func TestConnectionPool_ContextCancellation(t *testing.T) {
 	conn, err := pool.Get(context.Background())
 	require.NoError(t, err)
 
-	// Try to get another with cancelled context
+	// Try to get another with canceled context
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel() // Cancel immediately
 

internal/cache/backends/resp.go

@@ -44,7 +44,7 @@ type RESPWriter struct {
 
 // NewRESPWriter creates a new RESP writer from the pool (memory optimized)
 func NewRESPWriter(w io.Writer) *RESPWriter {
-	writer := writerPool.Get().(*RESPWriter)
+	writer, _ := writerPool.Get().(*RESPWriter)
 	writer.w = w
 	return writer
 }
@@ -80,7 +80,7 @@ type RESPReader struct {
 
 // NewRESPReader creates a new RESP reader from the pool (memory optimized)
 func NewRESPReader(r io.Reader) *RESPReader {
-	reader := readerPool.Get().(*RESPReader)
+	reader, _ := readerPool.Get().(*RESPReader)
 	reader.r.Reset(r)
 	return reader
 }

internal/cache/backends/singleflight.go

@@ -87,7 +87,7 @@ func (s *SingleflightCache) GetOrFetch(ctx context.Context, key string, fetcher
 	// If successful, store in cache
 	if call.err == nil && call.val != nil {
 		// Use a background context for cache storage to ensure it completes
-		// even if the original context is cancelled
+		// even if the original context is canceled
 		storeCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		_ = s.backend.Set(storeCtx, key, call.val, call.ttl)
 		cancel()

internal/cache/manager.go

@@ -232,7 +232,7 @@ func (m *Manager) Close() error {
 
 	var firstErr error
 
-	if err := m.tokenCache.Close(); err != nil && firstErr == nil {
+	if err := m.tokenCache.Close(); err != nil {
 		firstErr = err
 	}
 	if err := m.metadataCache.Close(); err != nil && firstErr == nil {