Feature Request: Detect and Optimize for Thin-Provisioned VMDKs

Feature Summary:
Enhance MigrateKit to detect thin-provisioned VMDKs and optionally optimize data transfer by skipping unused or zeroed blocks, reducing migration time and storage usage.

Why It's Needed:
Currently, MigrateKit transfers all allocated blocks, regardless of actual usage. For thin-provisioned disks, this leads to inefficiencies, especially when most of the disk is unused. Detecting thin-provisioned disks and integrating sparse-aware copy logic would make migrations faster and more bandwidth-efficient.

Proposed Enhancements:

Detection of VMDK type (thin/thick):

    Use pyVmomi to inspect VirtualDiskFlatVer2BackingInfo.thinProvisioned.

    Log provisioning type during pre-migration checks.

Sparse-aware Copying (Optional Feature Flag):

    Enable a --sparse-aware flag to:

        Skip zeroed blocks,

        Or use APIs that natively support sparse copies (if VDDK allows).

Logging & Warnings:

    Warn when thick disks are encountered (optional),

    Provide a report of total vs used disk space to visualize savings.

Benefits:

Reduced migration time,

Lower bandwidth usage,

Improved performance especially for large, thin-provisioned VMs.

Start by locating the pre-migration checks and current VMDK transfer path, then review how pyVmomi exposes VirtualDiskFlatVer2BackingInfo.thinProvisioned and whether VDDK supports sparse copies. Done means thin and thick disks are detected and logged, the --sparse-aware behavior is defined and validated, and reporting or warnings match the agreed scope.