Feature: Automatically disable part cooling fan on PAUSE

[zacharcc]

📌 Why should this be part of Mainsail?

• Many users expect the part cooling fan to turn off during a PAUSE, especially in cases like filament runout, color change, or print troubleshooting.
• Keeping the fan on is usually unnecessary and may be disruptive when handling filament changes or extruder adjustments.
• Because of this, many users will eventually try to modify the fan behavior themselves—whether successfully or not—to ensure it works as expected in future pauses.
• However, not all users are comfortable editing macros, and modifying complex Mainsail macros may lead to unintended issues.

Since most users will want this functionality anyway, it makes sense to include it as a default feature in client.cfg.

❌ Why not just use user_pause_macro?

• The user_pause_macro and user_resume_macro fields are designed for custom user-defined gcodes.
• If we use them for the fan control, users will lose flexibility because these fields will already be occupied.
• A built-in solution is cleaner and easier for users, especially for beginners.

✅ What this PR does:

• Automatically turns OFF the part cooling fan when PAUSE is triggered.
• Restores the previously set fan speed when RESUME is executed.

If you feel this should remain a user-defined feature, I understand and will respect your decision. However, I believe this is a simple and logical enhancement that aligns with user expectations.