Fix Stop button for slow models and terminal commands

- Added AbortSignal support to terminalRunner.ts to track and kill child processes
- Updated runProcess() to handle abort events and clean up process tracking
- Modified executeRunCommand() and handleToolCall() to accept and forward AbortSignal
- Updated runOneTool() to pass abort signal from ChatViewProvider
- handleStop() now calls stopAllRunningProcesses() to terminate all running commands
- Added stopAllRunningProcesses() utility to cancel all tracked processes

Version: 1.6.2 → 1.7.0 (minor, 4 source files modified)
