Function resolve_service_impacts 

pub fn resolve_service_impacts(
    items: &[PackageItem],
    action: PreflightAction,
) -> Vec<ServiceImpact>

What: Resolve systemd service impacts for the selected transaction items.

Inputs:

• items: Packages being installed or removed.
• action: Preflight action (install/update vs. remove).

Output:

• Vector of ServiceImpact entries representing impacted systemd units.

Details:

• Inspects pacman -Fl output for each package to find shipped unit files.
• Determines which units are currently active via systemctl list-units.
• Heuristically detects binaries that impact active units, even without unit files.
• Computes a recommended restart decision; defaults to defer when the unit is inactive or the action is a removal.