feat: Improve interactive CLI Ctrl+C handling

[monotykamary]

This pull request enhances the Ctrl+C (KeyboardInterrupt) handling within the interactive CLI to provide a more robust and user-friendly experience.

Changes Implemented:

1. Graceful Cancellation at Input Prompt (src/mcp_agent/core/enhanced_prompt.py):

   • Previously, pressing Ctrl+C while at the interactive input prompt (agent_name >) would cause the get_enhanced_input function to return "STOP", leading to the termination of the entire interactive session.
   • This has been modified so that a KeyboardInterrupt at the input prompt now results in:
     • A message: [yellow]Input cancelled. Type a command or 'STOP' to exit session.[/yellow]
     • The input field being cleared.
     • The interactive session continuing, allowing the user to enter a new command.

2. Cancellable Agent Tasks & Session Continuation (src/mcp_agent/core/interactive_prompt.py):

   • Added import asyncio for asyncio.CancelledError.
   • The prompt_loop now wraps the call to await send_func(...) (which executes agent tasks) in a try...except block.
   • This block catches KeyboardInterrupt (from Ctrl+C) and asyncio.CancelledError that might occur during an ongoing agent operation (e.g., a long LLM call).
   • Upon catching such an interruption:
     • A message is displayed (e.g., [yellow]Request cancelled by user (Ctrl+C).[/yellow] or [yellow]Request task was cancelled.[/yellow]).
     • An attempt is made to stop and clear any active rich.progress display to prevent visual artifacts.
     • The interactive loop continues, meaning the user is returned to a fresh input prompt, and the session remains active.

Impact:

• Users can now safely press Ctrl+C at the input prompt without unintentionally exiting their interactive session.
• Long-running agent tasks can be interrupted using Ctrl+C, and the user can immediately issue new commands within the same session, significantly improving workflow efficiency and responsiveness.

These changes address the issue where Ctrl+C would always terminate the interactive session, regardless of whether it was pressed at the prompt or during an agent's operation. The new behavior allows for more fine-grained control and a less disruptive user experience.

[evalstate]

Hi @monotykamary -- would you mind taking a look at the check failures on these PRs please? TY!