feat: implement multisig security layer and pet ownership history

[mansory-01]

This PR implements multisignature (MultiSig) security system for operations and a tracking system for pet ownership history.

---

Changes

Multi-Admin Security (MultiSig)

• Decentralized Governance — Transitioned from a single-admin model to a multi-administrator system with a configurable approval threshold
• Structured Proposals — Introduced a propose → approve → execute workflow for sensitive actions including Contract Upgrades, Vet Verification, and Admin Changes.
• Security Safeguards — Each proposal includes a configurable expiry time and strict authorization checks using standard Soroban require_auth() patterns.

Ownership History Tracking

• Immutable Lineage — Implemented a tracking system that records every ownership transfer, capturing the previous owner, new owner, timestamp, and transfer reason.
• Transfer-Acceptance Flow — Updated pet transfer logic to require the new owner's explicit acceptance, ensuring transparency and preventing accidental transfers.

Code Quality & Compatibility

• Soroban Best Practices — Refactored enums to use tuple variants for better compatibility with #[contracttype].

---

Checklist

• Implement MultiSig infrastructure (propose_action, approve_proposal, execute_proposal)
• Integrate MultiSig into critical paths (Vet registration and license revocation)
• Add ownership history recording to the accept_pet_transfer flow
• Implement get_ownership_history for full record auditability
• Add unit tests covering thresholds, expiries, and history tracking

closes #119
closes #115

[llinsss]

plese you have alot of conflicts. kindly resolve

[llinsss]

you have merge conflicts. please resolve