Implement `change_freelancer` logic

[meshackyaro]

Description

This issue aims to address the implementation of Implement change_freelancer logic.

The core objective is to: Allow the client to switch to a different freelancer if the current one mutually agrees.

By completing this feature, we will ensure that the TrustFlow protocol maintains its high standards for security, usability, and decentralized logic. This issue requires careful attention to the Smart Contracts architecture and adherence to the existing project conventions.

When picking up this issue, please ensure you document any new dependencies or architectural decisions made during development.

Component

Smart Contracts

Difficulty

🟡 Medium

Tasks

• Review Soroban architecture and soroban-cli usage
• Implement Rust logic for: Implement change_freelancer logic
• Write comprehensive unit tests in Rust
• Ensure proper event emission for indexing
• Run cargo fmt and cargo clippy
• Verify soroban contract build successfully compiles to WASM without bloating size

Acceptance Criteria

• Feature accurately implements the objective: Allow the client to switch to a different freelancer if the current one mutually agrees.
• Any PR that introduces TypeScript/Rust errors is automatically blocked
• CI pipeline runs in under 3 minutes per PR
• Code is properly reviewed and approved by codeowners

Estimated Time

4-8 hours