changed async-nats-easy to nats-handling

Created by: oblivisheee

This pull request involves replacing the async-nats-easy library with the nats-handling library across multiple files and modules in the project. The changes include updating dependencies, modifying error handling, and refactoring code to use the new library.

Dependency updates:

• assistant/Cargo.toml, subscription/Cargo.toml, users/Cargo.toml: Removed async-nats-easy and added nats-handling as a dependency. [1] [2] [3] [4] [5]

Error handling updates:

• assistant/src/errors.rs, subscription/src/errors.rs, users/src/errors.rs: Updated error handling to use nats_handling::NatsError instead of async_nats_easy::NatsError. [1] [2] [3] [4]

Code refactoring:

• assistant/src/main.rs, subscription/src/main.rs, users/src/main.rs: Replaced instances of async_nats_easy with nats_handling for NATS client initialization and message processing. [1] [2] [3] [4] [5] [6]
• assistant/src/nats.rs, subscription/src/nats.rs, users/src/nats.rs: Updated imports and refactored message processing logic to use nats_handling library functions. [1] [2] [3] [4] [5]