Changed from one large WALK query with all OIDs to separate WALK queries
per table type. This prevents a failure in one unsupported table (like ARP
on a device that doesn't support it) from killing the entire polling
operation.
Before: Single WALK with neighbor + ARP + MAC + IP + HOST-RESOURCES OIDs
After: Separate WALKs for each table type
This makes polling more resilient - if a device doesn't support ARP tables
or HOST-RESOURCES-MIB, those WALKs will fail individually while neighbors,
MAC tables, and IP addresses can still succeed.
Fixes agent errors where a single SNMP receive error was killing the
entire poller thread and failing all subsequent operations with
'Poller thread died'.