feat(client): Improve initialization state handling in McpAsyncClient (#39)

- Add proper initialization state tracking using AtomicBoolean and Sinks
- Implement timeout handling for requests requiring initialization
- Ensure all client methods verify initialization state before proceeding
- Fix rootsListChangedNotification to check initialization state
- Improve error messages for uninitialized client operations
- improve JavaDoc
- Add tests to verify proper error handling for uninitialized clients
  - Replace hardcoded timeout constants with configurable getTimeoutDuration() method
  - Remove automatic initialization in setUp methods to allow explicit testing

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>