Implement Multi-Token Reward Support

[Mkalbani]

Description

The current reward system only supports a single token type. This limits quest design flexibility.

Expected Behavior

Quest creators should be able to configure ERC-20, ERC-721, and native token rewards in a single quest.

Proposed Changes

• Extend the reward struct to include tokenType (enum: NATIVE, ERC20, ERC721)
• Update payout logic to handle each token type accordingly

Acceptance Criteria

• Reward struct supports multiple token types
• Payout correctly handles ERC-20, ERC-721, and native tokens
• Unit tests for each reward type

[wokedi]

@wokedi has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, i have gone through the task description and will like to work on this please. ETA: 8hours. Thank you

ℹ️ Repo Maintainers: To accept this application, review their application or assign @wokedi to this issue.