feat: add Import-PveVmDisk cmdlet for disk image import

Imports disk images (qcow2, raw, vmdk) and OVA archives into VMs
via the PVE API using POST config with import-from syntax.

- VmService.ImportDisk() method using POST /nodes/{node}/qemu/{vmid}/config
- Import-PveVmDisk cmdlet with -Source, -Disk, -TargetStorage, -Format, -Wait
- Pester unit tests
- prepare-test-vm.sh updated to use Import-PveVmDisk instead of SSH qm importdisk
- Set-PveNetwork: add required Type parameter (fixes PVE API 400 error)
- Integration test fix: pass -Type bridge to Set-PveNetwork

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

README.md

@@ -227,6 +227,7 @@ SDN management requires Proxmox VE 8.0 or later. Connected server is version 7.4
 | `Get-PveVmConfig` | Get VM configuration |
 | `Set-PveVmConfig` | Modify VM configuration |
 | `Resize-PveVmDisk` | Resize a VM disk |
+| `Import-PveVmDisk` | Import a disk image (qcow2, raw, vmdk, OVA) into a VM |
 
 ### Containers
 | Cmdlet | Description |