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

refresh_coordinator.go

@@ -234,7 +234,7 @@ func (rc *RefreshCoordinator) CoordinateRefresh(
 // Returns (operation, false, nil) if joined an existing operation
 // Returns (nil, false, error) if the operation was rejected
 func (rc *RefreshCoordinator) getOrCreateOperation(
-	ctx context.Context,
+	_ context.Context,
 	sessionID string,
 	tokenHash string,
 	refreshToken string,
@@ -293,7 +293,7 @@ func (rc *RefreshCoordinator) getOrCreateOperation(
 // executeRefreshAsync performs the actual refresh operation asynchronously
 func (rc *RefreshCoordinator) executeRefreshAsync(
 	operation *refreshOperation,
-	sessionID string,
+	_ string, // sessionID - reserved for future metrics/logging
 	tokenHash string,
 	refreshFunc func() (*TokenResponse, error),
 ) {