Remove redundant incus_ prefix from root module variables

Rename variables to remove the useless incus_ prefix:
- incus_hypervisors → hypervisors
- incus_witnesses → witnesses
- incus_token → token
- incus_networks → networks
- incus_storage_pools → storage_pools

Updates all references across provider.tf, groups.tf, network.tf,
storage.tf, and .auto.tfvars files.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

incus/network.tf

@@ -1,10 +1,10 @@
 module "network" {
   source            = "./modules/network"
-  for_each          = var.incus_networks
+  for_each          = var.networks
   name              = each.key
   type              = each.value.type
-  hypervisors       = toset(keys(var.incus_hypervisors))
-  witnesses         = toset(keys(var.incus_witnesses))
+  hypervisors       = toset(keys(var.hypervisors))
+  witnesses         = toset(keys(var.witnesses))
   hypervisor_config = each.value.hypervisor_config
   witness_config    = each.value.witness_config
 }