🪲 BUG-#131: Fix timeout thread leak in ThreadPoolExecutor

[FernandoCelmer]

Description

• dotflow/core/action.py — Replace with ThreadPoolExecutor context manager with explicit shutdown(wait=False, cancel_futures=True) on timeout

Motivation and Context

When future.result(timeout=...) raises TimeoutError, the with block calls executor.shutdown(wait=True) which blocks until the thread finishes. If the thread is stuck, the entire workflow hangs. The fix uses shutdown(wait=False, cancel_futures=True) to release resources without blocking.

Closes #131

Types of changes

• Bug fix (change that fixes an issue)
• New feature (change which adds functionality)
• Documentation

Checklist

• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• I have updated the CHANGELOG
• I have updated the documentation accordingly