🪲 BUG-#140: Fix race condition, thread tracking, and signal handler restoration in SchedulerCron

[FernandoCelmer]

Description

• dotflow/providers/scheduler_cron.py — Three fixes for SchedulerCron

Fix 1 — Race condition in queue overlap (#140)

Move thread creation decision inside the lock in _execute_queued. The thread object is created under the lock and started after release, closing the window where _dispatch_queue could modify _queue_count.

Fix 2 — Daemon threads never joined (#142)

Track all spawned threads in _threads list. stop() now joins all in-flight threads with an optional timeout before returning.

Fix 3 — Signal handlers overwritten globally (#144)

Save previous SIGINT/SIGTERM handlers in _register_signals. Restore them in _restore_signals called from stop().

Closes #140
Closes #142
Closes #144

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