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/recovery/metrics_test.go

@@ -223,7 +223,7 @@ func TestRetryExecutor_ExecuteWithContext_ContextCancelled(t *testing.T) {
 	wg.Wait()
 
 	if execErr == nil {
-		t.Error("Expected error when context is cancelled")
+		t.Error("Expected error when context is canceled")
 	}
 }
 
@@ -240,7 +240,7 @@ func TestRetryExecutor_ExecuteWithContext_ContextCancelledBeforeStart(t *testing
 	})
 
 	if err == nil {
-		t.Error("Expected error when context is already cancelled")
+		t.Error("Expected error when context is already canceled")
 	}
 }
 
@@ -282,7 +282,7 @@ func TestRetryExecutor_isRetryableError(t *testing.T) {
 		{name: "timeout", err: errors.New("TIMEOUT"), expected: true}, // case insensitive
 		{name: "EOF", err: errors.New("EOF"), expected: false},
 		{name: "random error", err: errors.New("something else"), expected: false},
-		{name: "context cancelled", err: context.Canceled, expected: false},
+		{name: "context canceled", err: context.Canceled, expected: false},
 		{name: "context deadline exceeded", err: context.DeadlineExceeded, expected: false},
 	}