enhance: cleanup env on close session

[a7m-1st]

fixes #883

Description

• Track toolkits for cleanup in registered_toolkits
• Enhance cleanup function to remove env too in TerminalToolkit extension

Notes

• I think we need to enhance the base TErminalToolkit.cleanup() to also remove the self.cloned_env_path
• the clone_current_env inccurs larger env due to reusing the parent one
• This pr doesn't solve the [BUG] Backend stalled while initializing workforce agents #864 where it still takes time to setup the env

• Perhaps a smart trick to increase the speed of the env setup is to use the parent as reference path on UV? --cache-dir and/or direction all task instances to the same path via uv --directory ./shared_terminal per project?

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

[a7m-1st]

On timeout