pkg/driver/vz: Support ASIF as diffdisk

[norio-nomura]

Depends on lima-vm/go-qcow2reader#61

• Add LIMA_VZ_ASIF environment variable to use ASIF on creating diffdisk
• Add vmType.vz.diskImageFormat that accepts "raw" or "asif"

vmOpts:
  vz:
    diskImageFormat: null
    # Specify the disk image format: "raw" or "asif".
    # Currently only applies to the primary disk image.
    # "asif" requires macOS 26+, and does not support converting back to "raw".
    # 🟢 Builtin default: "raw"

• pkg/imgutil: Change ImageDiskManager.ConvertToRaw() to ImageDiskManager.ConvertToRaw() that accepts raw.Type or asif.Type

Hide obsolete description

How to setup ASIF as diffdisk:

1. Create an instance for test, then stop it.

$ limactl start template:ubuntu --name=asif-test --tty=false --log-level=fatal; limactl stop asif-test --log-level=fatal

2. Convert diffdisk with ASIF image. (original will be renamed to diffdisk.raw)

$ hack/convert-diffdisk-to-asif.sh asif-test
+ instance=asif-test
++ limactl list asif-test --format '{{.Dir}}'
+ instance_dir=/Users/norio/.lima/asif-test
++ head -c 4 /Users/norio/.lima/asif-test/diffdisk
+ head4bytes=
+ case "${head4bytes}" in
++ limactl list asif-test --format '{{.Status}}'
+ instance_state=Stopped
+ [[ Stopped == \S\t\o\p\p\e\d ]]
+ diskutil image create blank --fs none --format ASIF --size 100GiB /Users/norio/.lima/asif-test/diffdisk.asif

/Users/norio/.lima/asif-test/diffdisk.asif created
++ diskutil image attach -n /Users/norio/.lima/asif-test/diffdisk.asif
+ attached_device=/dev/disk5
+ dd if=/Users/norio/.lima/asif-test/diffdisk of=/dev/disk5 status=progress conv=sparse
  107152496640 bytes (107 GB, 100 GiB) transferred 115.003s, 932 MB/s
209715200+0 records in
209715200+0 records out
107374182400 bytes transferred in 115.228413 secs (931837727 bytes/sec)
+ hdiutil detach /dev/disk5
"disk5" ejected.
+ mv /Users/norio/.lima/asif-test/diffdisk /Users/norio/.lima/asif-test/diffdisk.raw
+ mv /Users/norio/.lima/asif-test/diffdisk.asif /Users/norio/.lima/asif-test/diffdisk
+ echo 'Converted diffdisk to ASIF format successfully'
Converted diffdisk to ASIF format successfully

3. Start the instance

$ limactl start asif-test

[norio-nomura]

Implemented conversion to ASIF

[norio-nomura]

Expecting CI failures will be fixed by #4336 and #4341.

[norio-nomura]

Force pushed and updated PR description.

[norio-nomura]

https://github.com/lima-vm/lima/actions/runs/19491065038/job/55783186209?pr=4327#step:10:1084

TEST| [INFO] Testing cloning
...
time="2025-11-19T06:00:05Z" level=error msg="[hostagent] failed to copy file to disk nerdctl-full.tgz: write /home/runner/.lima/test-misc-clone/cidata.iso: no space left on device" fields.level=fatal

Does sparsing work on clone?