refactor: Address Copilot PR review feedback for production readiness

🔧 Improvements based on Copilot's code review:

✅ Removed debug print statements from production code
- Removed fmt.Printf debug statements from migrator.go FullDataTypeOf method
- Cleaned up production code to remove debug noise

✅ Implemented controlled debug logging system
- Added GORM_DUCKDB_DEBUG environment variable control
- Created debugLog() function that only logs when debug mode enabled
- Added errorLog() function for consistent error logging
- Replaced all log.Printf("[DEBUG]") with controlled debugLog() calls
- Replaced all log.Printf("[ERROR]") with errorLog() calls

✅ Fixed error handling in HasTable method
- Changed error masking (return nil) to proper error propagation (return err)
- Added descriptive error message for nil rows condition
- Improved debugging experience by preserving actual error information

🎯 Production Benefits:
- Cleaner production logs (no debug noise unless explicitly enabled)
- Better error debugging with proper error propagation
- Configurable logging via GORM_DUCKDB_DEBUG environment variable
- Maintained all functionality while improving code quality

Usage: Set GORM_DUCKDB_DEBUG=true to enable detailed debug logging

Author: greysquirr3l

custom_row_debug.go

@@ -1,51 +1,49 @@
 package duckdb
 
 import (
-	"log"
-
 	"gorm.io/gorm"
 )
 
 // CustomRowQuery is a debugging version of GORM's RowQuery callback
 func CustomRowQuery(db *gorm.DB) {
-	log.Printf("[DEBUG] CustomRowQuery called")
-	log.Printf("[DEBUG] db.Error: %v", db.Error)
-	log.Printf("[DEBUG] db.DryRun: %t", db.DryRun)
+	debugLog(" CustomRowQuery called")
+	debugLog(" db.Error: %v", db.Error)
+	debugLog(" db.DryRun: %t", db.DryRun)
 
 	if db.Error == nil {
-		log.Printf("[DEBUG] No error, calling BuildQuerySQL")
+		debugLog(" No error, calling BuildQuerySQL")
 		// This is what GORM's BuildQuerySQL does for Raw queries
 		if db.Statement.SQL.Len() == 0 {
-			log.Printf("[DEBUG] SQL is empty, this shouldn't happen for Raw() queries")
+			debugLog(" SQL is empty, this shouldn't happen for Raw() queries")
 		}
 
 		// Check for DryRun or Error before proceeding
 		if db.DryRun || db.Error != nil {
-			log.Printf("[DEBUG] DryRun=%t or Error=%v, returning early", db.DryRun, db.Error)
+			debugLog(" DryRun=%t or Error=%v, returning early", db.DryRun, db.Error)
 			return
 		}
 
-		log.Printf("[DEBUG] Checking for 'rows' setting")
+		debugLog(" Checking for 'rows' setting")
 		if isRows, ok := db.Get("rows"); ok && isRows.(bool) {
-			log.Printf("[DEBUG] isRows=true, calling QueryContext")
+			debugLog(" isRows=true, calling QueryContext")
 			db.Statement.Settings.Delete("rows")
 			db.Statement.Dest, db.Error = db.Statement.ConnPool.QueryContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
 		} else {
-			log.Printf("[DEBUG] isRows=false or not found, calling QueryRowContext")
-			log.Printf("[DEBUG] SQL: %s", db.Statement.SQL.String())
-			log.Printf("[DEBUG] Vars: %v", db.Statement.Vars)
-			log.Printf("[DEBUG] ConnPool type: %T", db.Statement.ConnPool)
+			debugLog(" isRows=false or not found, calling QueryRowContext")
+			debugLog(" SQL: %s", db.Statement.SQL.String())
+			debugLog(" Vars: %v", db.Statement.Vars)
+			debugLog(" ConnPool type: %T", db.Statement.ConnPool)
 
 			result := db.Statement.ConnPool.QueryRowContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
-			log.Printf("[DEBUG] QueryRowContext returned: %v (nil: %t)", result, result == nil)
+			debugLog(" QueryRowContext returned: %v (nil: %t)", result, result == nil)
 
 			db.Statement.Dest = result
-			log.Printf("[DEBUG] After assignment - Statement.Dest: %v (nil: %t)", db.Statement.Dest, db.Statement.Dest == nil)
+			debugLog(" After assignment - Statement.Dest: %v (nil: %t)", db.Statement.Dest, db.Statement.Dest == nil)
 		}
 
-		log.Printf("[DEBUG] Setting RowsAffected to -1")
+		debugLog(" Setting RowsAffected to -1")
 		db.RowsAffected = -1
 	} else {
-		log.Printf("[DEBUG] db.Error is not nil: %v", db.Error)
+		debugLog(" db.Error is not nil: %v", db.Error)
 	}
 }