refac: several unverified users can exist at once: an empty reset or verification code is stored as no value so it doesn't break the unique constraint, and deleting a user removes the row so the same username and email can register again

internal/infrastructure/persistence/models/userModel.go

@@ -2,19 +2,16 @@ package models
 
 import (
 	"time"
-
-	"gorm.io/gorm"
 )
 
 type User struct {
-	gorm.Model
-	ID                     uint32 `gorm:"primaryKey;autoIncrement"`
-	Username               string `gorm:"unique;not null"`
-	Password               string `gorm:"not null"`
-	PasswordResetCode      string `gorm:"unique"`
-	Email                  string `gorm:"unique;not null"`
-	IsVerified             bool   `gorm:"default=false;not null"`
-	VerificationCode       string `gorm:"unique"`
+	ID                     uint32  `gorm:"primaryKey;autoIncrement"`
+	Username               string  `gorm:"unique;not null"`
+	Password               string  `gorm:"not null"`
+	PasswordResetCode      *string `gorm:"unique"`
+	Email                  string  `gorm:"unique;not null"`
+	IsVerified             bool    `gorm:"default=false;not null"`
+	VerificationCode       *string `gorm:"unique"`
 	VerificationExpiration time.Time
 	CreatedAt              time.Time `gorm:"autoCreateTime"`
 	UpdatedAt              time.Time `gorm:"autoUpdateTime"`