block: add read-only VMDK disk image support

[ChengyuZhu6]

Introduce read-only VMDK (monolithicFlat) support using the imago library.

Changes

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Reason

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• This functionality cannot be added in rust-vmm.

[hsiangkao]

@ChengyuZhu6 what prevents this as a draft?

[ShadowCurse]

Hi @ChengyuZhu6, unfortunately we don't have enough bandwidth to review this for now.

[hsiangkao]

Hi @ChengyuZhu6, unfortunately we don't have enough bandwidth to review this for now.

@ShadowCurse I guess this one is not complicated and it seems almost half the change is test cases.
Since it uses imago library to handle vmdk format, I guess the remaining logic should be straight-forward?

Also I guess the commit message should be improved to make the usage clear at least.