fix(dvcr): VMDK import error

[hardcoretime]

Description

This PR fixes the issue with importing VMDK disk images into DVCR (Deckhouse Virtualization Container Registry).

Technical changes:

1. Early format detection: Modified getImageInfo() to detect VMDK format by reading the first 10MB and checking the magic number using image.Header.Match().

2. VMDK-specific processing: Implemented getImageInfoVMDK() that creates a synthetic sparse VMDK file from:

   • Head buffer (10MB) - contains VMDK header and initial metadata
   • Tail buffer (50MB) - contains footer, Grain Directory, and Grain Tables
   • Sparse hole in the middle - actual disk data (not needed for qemu-img info)

3. TailBuffer implementation: Added ring buffer that efficiently stores only the last N bytes from a stream without keeping the entire file in memory.

4. Better error diagnostics: Changed cmd.Output() to cmd.CombinedOutput() to capture stderr from qemu-img for debugging.

5. Separated processing paths:

   • getImageInfoVMDK() - for VMDK format using synthetic file approach
   • getImageInfoStandard() - for other formats (qcow2, iso, raw) using existing approach

Resource efficiency:

• VMDK images: Fixed 60MB memory footprint (10MB head + 50MB tail ring buffer) regardless of source VMDK size. Synthetic sparse file uses ~60MB disk space.
• Other formats: No changes, uses existing 64MB temp file approach.
• Benefit: Can process multi-gigabyte VMDK images with constant low memory usage.

Why do we need it, and what problem does it solve?

Problem:

When importing VMDK disk images (especially streamOptimized format commonly used in OVF/OVA exports from VMware), the import failed with error:

qemu-img: Could not open '/tmp/tempfile': Invalid footer
exit status 1

What is the expected result?

VMDK images import successfully.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: core
type: fix
summary: "Fixed the creation of block devices from VMDK files (especially for VMDKs in the `streamOptimized` format used in exports from VMware)."

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