Overhaul VirtFusion provider: 20 resources, 30 data sources, multipage pagination

Complete rewrite of the VirtFusion Terraform provider with full API coverage:

- 20 managed resources (server, build, SSH key, user, firewall, IP blocks, etc.)
- 30 data sources (hypervisors, packages, servers, IP blocks, self-service, etc.)
- New HTTP client with proper error handling, query parameter support, and
  automatic multipage pagination via GetAllPages (fetches all pages from
  Laravel-style paginated endpoints and merges into a single response)
- Fixed type mismatches against live API: ServerData.Suspended (int→bool),
  IPBlockData.Type (string→int), PackageData json tags (primaryStorage, etc.),
  ServerData nested CPU/Settings/Resources structure, HypervisorGroupResources
  array response
- Configurable results-per-page (default 300) on all list data sources
- Migrated CI from GitHub Actions to Gitea Actions
- Updated goreleaser config, go.mod dependencies, and examples

Verified against live VirtFusion instance at cp.vps.ezscale.tech:
all data sources return correct data with full pagination support.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/resources/virtfusion_server_build/resource.tf

@@ -0,0 +1,10 @@
+resource "virtfusion_server_build" "node1_build" {
+  server_id = virtfusion_server.node1.id
+  name      = "my-server"
+  hostname  = "my-server.example.com"
+  osid      = 1
+  vnc       = true
+  ipv6      = false
+  ssh_keys  = [virtfusion_ssh_key.mykey.id]
+  email     = false
+}