Implement token burn and deflationary mechanism

[Richiey1]

Overview

This PR implements a robust token burn and deflationary mechanism for the Quest project. It introduces a central token_burn controller and integrates it into the RewardToken contract.

Key Changes

• New token_burn Contract: Manages burn configurations (rate, enabled status), tracks total burned tokens by category (fees, voluntary, unlocks), and stores a paginated history of burn events.
• RewardToken Integration:
  • Added set_burn_controller to link the token to the burn mechanism.
  • Updated transfer and transfer_from to automatically apply transaction fee burns.
  • Updated burn and spend_for_unlock to record burns in the controller.
• Security & Stability:
  • Fixed deprecated invoker() method usage for Soroban v21.
  • Implemented dynamic contract invocation for cross-contract calls.
  • Added comprehensive unit and integration tests.

Verification

• Unit tests for token_burn passed.
• Integration tests for RewardToken burn flow passed.
• Verified total supply reduction on every burn event.

[Richiey1]

Important: Post-Deployment Activation

IMPORTANT
To activate the burn mechanism on-chain, ensure to call set_burn_controller on the RewardToken contract with the deployed token_burn contract address.
The deflationary logic remains dormant until this link is established, allowing for a two-stage deployment (Contract Deployment -> Controller Activation).

[Mkalbani]

@Richiey1 Please resolve conflict