Introduce a new helper function get_carp_entries() to retrieve CARP
configuration entries from pillar network data.
The function iterates over interfaces, filters FHRP entries using
the "carp" protocol, and returns structured and ordered data including:
- device (interface name)
- vhid
- vip
- advskew (defaulting to 0 when not specified)
Unit tests were added to validate:
- correct extraction of CARP entries when present,
- proper handling of empty FHRP lists
ref T2264