feat: add heartbeat to avoid unexpected timeout.

[youngsofun]

This PR introduces several key improvements to enhance connection management, resource cleanup, and observability across Python, JavaScript, and Rust bindings:

1. Introduce a global runtime to handle core background operations including heartbeat mechanisms, finalization, and logout procedures.

2. Implement a global background task that manages heartbeat checks for all active connections, ensuring persistent and reliable connections.

3. Add a close method to the RowIterator to enable explicit resource release, complementing automatic cleanup.

4. Enhance resource cleanup logic:

   • Send finalization signals when rows/cursors are dropped or closed (across Python, JavaScript, and Rust)
   • Trigger logout procedures when connections or cursors are dropped or closed (consistent across all bindings)

5. Initialize env_logger for JavaScript and Python bindings with a default log level of WARN. This provides a configurable debugging pathway via the RUST_LOG environment variable.

6. Ensure RowIterator maintains a reference to its parent Connection, preventing premature garbage collection of connections while iterators are in use.

[youngsofun]

@sundy-li @everpcpc please review