Use diskutil on macOS to extract volume name and path for FAT mounts

[mi-bear]

Summary

On macOS, this change improves the detection of FAT volumes by parsing diskutil info output to extract the volume name and path. This ensures accurate identification of mounted FAT-based filesystems under /Volumes.

Fixes #4519

Details

• Replaces hardcoded assumptions about the filesystem layout with dynamic parsing of diskutil info
• Extracts VolumeName and FileSystemPersonality for each mount point
• Adds a check for scanner.Err() to handle unexpected parsing issues gracefully
• Sorts results by volume path for consistent ordering

Platform

• This change only affects the darwin (macOS) platform
• No impact on other platforms or existing logic for linux/windows

[sago35]

Looks good to me.

[deadprogram]

Thank you for the improvement @mi-bear and to @sago35 & @b0ch3nski for review. Now squash/merging.