feat: implemented the multi-sig control for protocol fee parameters

[CollinsC1O]

Implementation Summary:

New Storage Symbols Added:

** FEE_ADMINS (Vec): Stores the list of addresses authorized to manage and modify fee parameters.
** FEE_THRESHOLD (u32): Stores the minimum number of multi-sig signers required to make fee modifications.
** configure_fee_multisig Introduced:

• Added a new function that allows the CONTRACT_ADMIN to configure the target fee_admins limit and to set a specific M-of-N threshold required to enact fee changes. This prevents unilateral fee rug-pulling and enforces community or multi-dev consensus.

Multi-Sig Logic Integrated into configure_fees:

Instead of a single admin parameter, configure_fees now takes an admins: Vec

array.

The contract dynamically iterates through the provided admins list to check if they belong to FEE_ADMINS.
On each matched valid admin, admin.require_auth() is called which enforces multi-signature confirmation natively using the Soroban auth framework.

Included robust safeguards against duplicate signatures/replay within the exact same configuration payload.
For backwards compatibility prior to multi-sig setup, it gracefully defaults to requiring the master CONTRACT_ADMIN.
Tests & Compilation:

The smart contract feature meets all required design patterns utilizing Soroban best practices!

Closes #515

Summary by CodeRabbit

Release Notes

• New Features

  • Implemented multi-signature fee governance system requiring collective approval from designated administrators to update fee configurations and treasury settings. Multiple admin addresses can now be configured with an approval threshold.

• Refactor

  • Refactored dispute resolution process to consolidate settlement logic and improve event emission timing.