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/provider.tf

@@ -9,14 +9,14 @@ terraform {
 provider "incus" {
   generate_client_certificates = true
   accept_remote_certificate    = true
-  default_remote               = keys(var.incus_hypervisors)[0]
+  default_remote               = keys(var.hypervisors)[0]
 
   dynamic "remote" {
-    for_each = var.incus_hypervisors
+    for_each = var.hypervisors
     content {
       name    = remote.key
       address = remote.value
-      token   = var.incus_token
+      token   = var.token
     }
   }
 }