FEAT/DOC: one line command to upgrade zarr to icechunk

[ianhi]

Problem

There should be a clean way to take an existing zarr store and transform it into an icechunk store via virtualization.

Proposed Solution

@TomNicholas reports that this can be done in 2 lines using virtualizarr.

We should wrap this for convenience in icechunk and do the following:

1. Document it prominently
2. provide as a function
3. provide in the cli

[TomNicholas]

this can be done in 2 lines using virtualizarr.

It can, but we might also want to consider doing it without virtualizarr, instead just in rust (using zarr-rs then .set_virtual_ref directly), because:

• It would keep to the theme of keeping IC logic in rust
• We can skip the overhead and deployment pain of python entirely
• It will probably be faster on large stores that require a lot of concurrency
• We don't need any of the concatenation or access features of VZ for this

Arguments for just wrapping VirtualiZarr:

• Faster development
• Reduces code duplication
• We know that will work, but the rust-only approach might not (e.g. if zarr-rs doesn't have a feature we need)

curious if you have thoughts @paraseba

[ianhi]

Any harm in the virtualizarr appraoch first, then moving to rust logic when we have more energy for it?

[TomNicholas]

No harm I don't think