Class based enums for PHP v4 for the subresources

[cb-alish]

🚀 Pull Request Template

📘 Description

There was a bug in the PHP SDK where enums for sub-resources were incorrectly marked as string instead of enum. This PR fixes that issue. We are introducing class based enums.

Before

    /**
    *
    * @var ?string $item_type
    */
    public ?string $item_type;

After

    /**
    *
    * @var ?\Chargebee\ClassBasedEnums\ItemType $item_type
    */
    public ?\Chargebee\ClassBasedEnums\ItemType $item_type;

Class definition

<?php

namespace Chargebee\ClassBasedEnums;

final class ItemType { 
    const PLAN = "plan";
    const ADDON = "addon";
    const CHARGE = "charge";
    const UNKNOWN = "unknown";

    private static array $choices = [ "plan","addon","charge", ];
    public final string $value;

    public static function tryFromValue(string $key): self
    {
        $instance = new self();
        $instance->value = self::isValidChoice($key) ? $key : self::UNKNOWN;

        return $instance;
    }
    public function __toString(): string
    {
        return $this->value;
    }
    private static function isValidChoice(string $key): bool
    {
        return in_array($key, self::$choices);
    }
}
?>

🧩 Related Issues / Tickets

Closes #IssueNumber

📂 Type of Change

• ✨ Feature
• 🐛 Bug Fix
• 📝 Documentation
• 🧪 Test Improvement
• 🔧 Refactor / Code Cleanup
• ⚙️ Build / Tooling

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